Teaching Paradox: Hearts of Iron IV, Part I: Operational Art

This week, at long last, we begin our long-delayed but always expected something that we blog for: the Hearts of Iron IV Teaching Paradox series!¹ This has been a long requested series that I put off for a long time because I wasn’t entirely sure how I wanted to tackle it. But my thoughts here have at least congealed somewhat.

So we are going to cover Paradox Interactive’s most popular strategy title: Hearts of Iron IV. And make no mistake: Hearts of Iron IV is popular, more so than any other Paradox game by some distance.² These days, Hearts of Iron IV generally has more concurrent players on Steam than even strategy stalwarts like Sid Meier’s Civilization (VI, because apparently no one likes VII), Age of Empires IV, Mount & Blade Bannerlord, etc. Hearts of Iron IV isn’t just the most popular Paradox game, it is the most popular strategy game – the whole genre – right now.³

And that makes its historical assumptions well worth talking about. This week we’re going to look at how Hearts of Iron IV simulates military operations, something that in practice makes up probably three-quarters of the player’s experience in the game. Then in the following weeks we’ll look at the strategic ‘shell’ around that operational core, with how the game understands industry, information, strategy and politics.

As with other entries in this series (Europa Universalis IV, Victoria II, Crusader Kings III and Imperator) the goal here isn’t a review of the game or a guide to it, but instead an effort to outline what the historical assumptions of a given game are, what its ‘theory of history’ is, and to try – to a degree – to assess that theory of history against what we actually know of the history.

Especially in this particular section, focused on how Hearts of Iron IV handles land combat, I found I struggled quite a bit to describe how the game simulates operations without getting pulled into how a player might design good operations. As a result, for HoI4 players, this first post may end up feeling a bit surface-level in its description of the game, but this is unavoidable: I want these posts to be intelligible to someone who has never played the game, after all. But whereas with other Paradox games I can often leave the ‘grand tactics’ of maneuvering armies out without losing too much of the core of the game, Hearts of Iron IV is almost all maneuvering armies. It thus cannot be left out, but at the same time, this is not the place for the minutiae of how to conduct an armored breakthrough.

Finally, I should note at the outset that while I bought my own copy of Hearts of Iron IV (ages ago) and have spent far too much money on its DLCs, Paradox did kindly provide me with copies of some of the expansion packs that were missing from my collection (mostly things in the second ‘Expansion pass’).

But first, if you like what you are reading here, please share it, as I rely on word of mouth to replenish my manpower pool after poorly considered post topics. If you really like it, you can support me, my academic work and my public writing, including this project on Patreon! I can’t promise to use your support to buy a division worth of tanks, but I also will not promise not to do that. If you want updates whenever a new post appears or want to hear my more bite-sized musings on history, security affairs and current events, you can follow me on Bluesky (@bretdevereaux.bsky.social). I am also active on Threads (bretdevereaux) and maintain a de minimis presence on Twitter (@bretdevereaux).

Operations

In past series on Paradox grand strategy titles, we’ve talked about how it is often possible to summarize these games (especially the way they are different from each other) in terms of what each game is ‘about’ – its core focus. Europa Universalis IV is a game about states,⁴ while Crusader Kings III is a game about personalistic rule and thus the personal relationships that define it and Victoria II is a game about pops (while Victoria III lives at the intersection of pops, economics and politics). That isn’t to say these games don’t include other things of course, but there is a clear central concept, an idea the game wants to explore most.

Hearts of Iron IV is a game about what in military theory we call operations. Indeed it is substantially more focused on operations than its predecessors (Hearts of Iron II and III; I never played the original Hearts of Iron and so won’t comment on it here) in that it streamlines everything but operations (e.g. research, industry, politics, espionage) in order to more clearly focus on the game’s major focus (though it then allows you to automate a fair chunk of the operations to try to control the complexity).

Now talking about this a bit tricky, because I want to say that Hearts of Iron IV is fundamentally about what we might call the operational level of military analysis or even the operational level of war. But the idea that there is a distinct operational ‘level,’ despite being part of United States military doctrine, is disputed by some current military theorists (if you want to read perhaps the clearest such dispute, see B.A. Friedman, On Operations: Operational Art and Military Disciplines (2021), which I find very persuasive on most of its point). But I don’t want to bog us down unpacking those arguments, which have to do with the nature of operations, the degree to which operational planning is actually a kind of ‘grand tactics,’ or the history of the idea (or lack of it) in Soviet ‘Deep Operation‘ doctrine.

And I don’t think I have to, because there may or may not really be an ‘operational level’ of war between tactics and strategy, but ‘operational art’ as commonly understood in the West is the focus of Hearts of Iron IV, so the term is useful for us regardless of its applicability to real war. Though, of course, the fact that it remains common in modern military doctrine should suggest that it is, to some degree, applicable.⁵

So what do we mean when we say ‘operations,’ ‘operational art’ or even an ‘operational level of war?’ We have discussed the three levels of military analysis a few times on the blog, but it has been a while and so is worth reviewing. The three levels are tactics (how you fight), operations (where you fight) and strategy (why you fight). To expand on those shorthand definitions, tactics (the lowest layer of analysis) concerns the method used to win battles (broadly defined): maneuver, positioning, stratagems, and so on. Strategy (the uppermost layer) considers the overall objectives a state, polity or organization has, the ways those objectives can be achieved (including the decision not to have a war) and the resources required to achieve those objectives, a set of components short-handed in US military doctrine as ‘Ends, Ways and Means.’ Grand strategy is sometimes treated as its own layer, which broadens the analysis to include political, diplomatic and economic tools and concerns, though I would tend to argue that all strategy is grand strategy: states do not have ends, ways or means that are ever wholly divorced from political, diplomatic and economic tools.

In this schema, operations is the layer that knits strategy together with tactics. Ideally the decision-making process begins with strategy, where it is determined that the best (or perhaps only) way to achieve to achieve a strategic end-state is through warfare. Operations is thus occupied with the question of how to reach that strategic end-state, whatever it might be, through the use of military force.

In practice, that generally means that operations takes the strategic end-state (‘compel the surrender of Germany’) and then designs military campaigns to achieve that objective, which of course means first asking, ‘what would cause Germany to surrender?’ Often this means making decisions about what theaters to prioritize (‘should I fight in France or in North Africa or in Italy?’), which all of the follow-on considerations of logistics, transport and movement in space and time. The maneuver component of this – planning the movement of often very large armies over vast spaces – strongly resembles a sort of ‘super-sized tactics’ and indeed the idea is often termed ‘grand tactics’ which in some contexts has a similar meaning.

Perhaps the best way to exemplify this is with a reasonably direct example, so let us posit Napoleon’s Ulm Campaign (1805). Napoleon had decided that he needed to knock Austria out of the war (‘ends’) and that the best way to do this was the destruction of Austria and Russia’s armies, with Austria coming first, (‘ways’) using Napoleon’s army (‘means’) – all strategic level concerns.

Now comes the operational art: how to best employ his army (the means) to those ends. Napoleon opts for a campaign of rapid maneuver so that he could concentrate a much larger French army against a smaller and isolated Austrian army before Russian (or other Austrian) help could arrive. To do that, he would have to march each piece of his army (his army corps, of which he had six in motion for the campaign) along separate routes (to make maximum use of roads and supplies), while carefully managing their movement (‘space and time’) to make sure they all arrived where the Austrians were at the same time (to avoid being picked off one by one). At the same time, managing the dispersed movement of several large armies meant managing the logistics of these forces, as the campaign would last almost a month (and could have lasted longer) in hostile territory.

Finally, the question of how to actually beat the Austrians once Napoleon’s forces arrived would be a question of tactics.

Operations is thus often concerned with the use of maneuver (both the ‘where’ and the ‘how fast’), logistics and terrain to create favorable conditions where battles can both be won and also be decisive or at least contribute to strategic ends. Now as a ‘level of war’ coequal with strategy and tactics, operations can and indeed must be more than just that, because it would have to consider uses of force beyond simply maneuvering against enemy armies in the field for the purpose of battles, but that frame will serve us pretty well here because it is the frame Hearts of Iron adopts across the entire series. Which is not a critique: this is a game about World War II, which was very substantially a war concerned with large conventional armies maneuvering in the field.

It is thus perhaps both ironic and telling that Hearts of Iron, arguably the modern military strategy game, is fundamentally a game about operations, not strategy (though the latter is present).

Divisions and Lines

Perhaps the most immediately striking and overwhelming element of HoI4‘s visual presentation is how it simulates and represents armies in order to facilitate a game about operations. Whereas in other Paradox titles, armies generally exist as a single ‘stack’ that occupies one point on the map (a province, for instance), in HoI4 (and the earlier HoI titles) armies are broken out into divisions, which, rather than being concentrated at a single point on the map, are instead spread out, typically in clear front lines, often along borders.

There are a few mechanics that push players towards this different way of organizing armies. First, whereas other Paradox games feature ‘armies’ as ‘stacks’ (groups that operate as one) of units, HoI4 treats the division as an almost ‘atomic’ unit. While divisions are (in ways we’ll get to) composed of smaller units, they cannot be merged or split apart and while they can be put in the same province they cannot be ‘stacked.’ A division which is defeated in a combat will not wait for the other divisions in the same combat to be defeated, but will retreat all on its own. In practice, the division functions as a UI element the same way an entire army ‘stack’ in Paradox’s other games does. The player is thus strongly encouraged to think about divisions as the ‘base unit’ of their operational approach (with implications in both nature and scale we’ll get to).

Moreover, the game gives players a lot of reasons not to group their divisions up. Battles, when they occur, have limited frontage and inflict penalties (both frontage penalties and stacking penalties) if there are too many divisions involved in the combat; at the very least excess divisions cannot participate (but have their organization, strength recovery and movement frozen), which makes it a bad use to have excess divisions in a single engagement.

But perhaps most significantly the logistics system compels spread out as well: divisions in Hearts of Iron IV do not just draw from the supply capacity of the province they’re in (they’re already mostly too big!), but rather they pull from a nearby supply hub (which may be several provinces away) and thus need a clear, friendly path to that supply hub. Supply hubs, in turn, have a limited capacity to support units. They can – in a system we’ll talk about later in the series – draw supply at greater distance, but that throughput is limited. Consequently, most states already have armies too large to be supported by a single supply hub. As a result the AI and the player generally cannot ‘doomstack’ (place all or nearly all of their combat units in a single, massive formation, located all together) as in other strategy titles. The player is forced to spread their divisions over multiple supply hubs to maintain them.

Even more importantly, far more so than in almost any other mainstream strategy game, it is very bad if enemies get behind you in Hearts of Iron IV. An enemy division between your divisions and your supply hubs blocks their supply, forcing them out of supply, with catastrophic penalties to combat power and steady attrition which depletes their equipment. Indeed much of the (grand) tactics of Hearts of Iron IV is about finding ways to isolate enemy units from their sources of logistics (which makes sense as this is a core element of operational art). Consequently most of the time, the player or AI will want to leave no gaps in their lines which might allow enemy units to encircle them.

Finally, that ‘no gaps’ approach is facilitated by HoI4‘s ‘movement is attack’ design, which is shares with no other mainland Paradox series. In every other Paradox game, for one army to attack another, it must arrive in the same province, but in Hearts of Iron (the whole series) a division initiates combat the moment it begins to enter a province with an enemy division and cannot finish moving into that province until it has won the battle, displacing the enemy division out of the province (by depleting its organization, forcing its retreat).

The result is a very different combat system, where wars (or at least theaters in wars) resemble two lines of divisions stretching over many provinces ‘shoving’ each other with offensive battles, as opposed to the ‘point location’ battles of other Paradox titles or indeed, other strategy games (e.g. the Total War series) more generally.

Iron Operations

The result is that ‘battles’ (large-scale engagement consisting of multiple attacks over connected provinces, the way we’d understand the ‘Battle of France’ or the ‘Battle of Stalingrad’ given their scale) in Hearts of Iron IV are a lot more granular than in other Paradox titles. In Europa Universalis, the player puts together an army, throws it against the enemy army and then hopes for the best: the outcome is heavily shaped by army composition, local terrain and such, but once the player has made the decision to offer battle (or been trapped into it), their active participation is over.

By contrast, HoI4 presents the player with a lot more decisions. Not just ‘should I have a battle in this theater’ but ‘which provinces specifically in this line should I attack first? Which divisions should I use? Should my attacks be sequential or coordinated? How many angles can I attack from?’ and so on. And that is before considering the impact of air or naval operations on the above. The result is something quite like tactics: a skilled player can – by considering attack directions, which divisions to use, local terrain, logistics considerations and so on – produce far more successful offensives in a way that the player simply doesn’t have that level of control in other Paradox titles.⁶

That said, the player isn’t really doing ‘tactics’ in a typical sense either (indeed in the game ‘tactics’ are approaches chosen automatically by your simulated generals during an engagement; they’re an explicit part of the game design simulated beneath your (operational) layer). The typical considerations of tactics – use of terrain, overlapping fields of fire, formations, fortifications, small-scale maneuver, suppression and so on – are at most simulated abstractly through various bonuses and penalties we’ll get to when we discuss the game’s approach to doctrine.

Because the player’s basic unit of control is the division (and indeed, the player cannot control anything smaller!) and divisions in WWII were really big, often as large or larger as entire field armies in earlier periods. Divisions vary substantially in size but range from 10,000 to 25,000 troops. To give a brief sense of how big a formation that is: most readers are probably familiar with E “EZ” Company from Band of Brothers; we see them do tactics (flanking, encirclement, suppression-and-maneuver). E Company probably feels to most folks like a big-ish unit, with a lot of people (around 140 at any given time) that we meet. E Company was, in fact, just one company (of three) in the 2nd battalion (of three) in the 506th Parachute Infantry regiment (of four, plus a host of supporting elements) in the 101st Airborne Division (which at a typical strength of ~8,000, including support elements, was a small division; US airborne divisions tended to be about half the size of regular infantry divisions). There were, in fact, four E Companies in the 101st, along with one E Battery.

In short, divisions are really big and as a result the concerns for a player whose smallest unit of control is an entire division look pretty different from unit tactics for squads, platoons or companies.

This is also shaped by HoI4‘s different combat model. As we’ve actually discussed before, in most strategy games, battles tend to be extremely decisive, with armies generally taking enormous casualties that render the loser immediately combat incapable. By contrast, in Hearts of Iron, each division has two kinds of ‘health’: a strength rating, which represents the proportion of equipment and manpower the division has available, and an organization rating, which represents the division’s combat effectiveness. Divisions are forced to retreat from combat when their organization hits zero and most damage accrues to organization rather than to strength. But organization replenishes quickly on the game’s time scale (measured in hours). The result is that a division, attacked and defeated by an infantry division, will generally have regenerated its organization substantially by the time it has retreated to the next province and thus be ready to defend again.⁷ Meanwhile strength damage, assuming the manpower and equipment is available in the country’s stockpile and the logistics route is clear, is replenished very fast compared to the rate at which divisions take strength losses (because most damage accrues to organization), with the result that recently ‘pushed’ divisions will also generally be at full strength.

This produces a ‘shoving match’ rather than decisive battles in HoI4‘s combat model: you do not (generally) destroy enemy divisions when you defeat them, you merely push them. The only reliable way to destroy an enemy division entirely is to defeat it when it has nowhere else to retreat, generally by encircling it. It is, of course, still possible to adopt an attritional strategy, simply aiming to deplete the enemy’s stockpile of manpower and equipment faster than your own – and that does sometimes happen – but what the player is generally trying to do is to use operational art to move faster than that, either by accelerating attrition or bypassing it altogether. But the tool to do that is taking and holding ground (provinces), which neatly reorients the players attention to the way that decision-makers at the time thought about it: operations to take or hold specific territory (rather than thinking, in the first instance, about destroying a given army).

The player’s task, then (which the AI mimics) is to ask, “how do I both achieve shoving (how do I get the front moving the way I want in the first place) and how do I then move the front line in a way that achieves some greater objective?” It is that latter part that is such a shift because, recall, in a lot of games of this sort simply destroying the enemy is the objective, but in Hearts of Iron IV, the enemy will not be destroyed (probably), merely moved backwards. So the question becomes not ‘how do I destroy the enemy?’ but ‘how do I move them backwards in a way that gets me closer to winning?‘

In short, the player is asking, ‘how do I bridge the gap between my tactics (being able to shove the enemy) and my strategy (winning the war in a way that achieves my objectives).’ Which (said gesturing upwards energetically) is operations!

Now I don’t want to get too deep here into ‘how do be good at Hearts of Iron‘ but there are a number of different mid-term objectives players might aim to ‘shove’ for. Perhaps the nearest term is ‘shoving’ for a better vantage to attack a key location. Cities, mountains, forts, forests and so on can all be really good defensive locations; rivers act as barriers between provinces which disadvantage attacks over them. At the scale HoI4 exists at, you cannot ‘flank’ these positions (you can encircle them, more on that in a second), however attacking one province simultaneously from multiple directions widens the frontage of the battle, allowing the attacker to get more divisions into the fray, which can offset the defender’s terrain advantage.⁸ So often the first objective of a ‘shove’ is to clear ‘easier’ provinces (plains, hills, ones not guarded by river-crossings) in order to be able to lever an opponent out of the ‘hard’ provinces.

One step up further than that, the player might aim to break out into enemy rear areas and disrupt logistics. As noted above, units need clear, unobstructed path to a friendly supply hub to fight effectively: seizing that hub or pinching the supply route (say, cutting across a key rail line) can render even very favorable positions untenable.⁹ The extreme version of this is encirclement, where you ‘shove’ in a way that cuts off part of the enemy army from any route to their capital, which puts them out of supply (with major combat penalties) and creates a pocket. If the player can then close down that pocket (weakened by attrition and supply penalties as the divisions in it cannot be reinforced), left nowhere to run the divisions stuck in the pocket will be destroyed when they can no longer retreat. This is the one reliably way to fully destroy a division (along with all of its manpower and equipment) and thus the most powerful way to shift the balance of attrition in your favor.¹⁰

Perhaps most importantly, of course, you can want to ‘shove’ in order to get control over the underlying terrain itself. As we’ll get to later, factories and raw materials in Hearts of Iron IV do not exist abstractly, they live on the map in specific places – seizing a key area denies the factories and resources in that area to your enemy, further accelerating an attritional advantage. Key urban centers also are ‘victory point’ locations: countries are compelled to surrender (capitulate) when a certain majority (typically quite high) of their victory points are taken.

In some cases, a player may expect to defeat an enemy with a single big initial offensive – a coup de main – in which case the offensive design is about navigating divisions to key victory points and seizing them while maintaining and protecting the logistics lines that effort creates. But in most cases, it is going to take several ‘shoves’ to achieve victory and attrition is going to play a role. Consequently, the player might instead plan a single large campaign aiming to seize a key resource zone or industrial area (and finish up with a front line anchored on good defensive terrain for the inevitable counter-attack), which in turn is composed of smaller operations levering the enemy out of the area by seizing logistics hubs or through disruption which is in turn composed of smaller battles that get the front moving and set terrain conditions for successfully attacking key enemy strong-points.

In short, the player in Hearts of Iron IV lives in the space between strategy (‘win the war’ – as we’ll see, HoI4‘s strategic layer is actually much less developed than comparable games like Victoria III or Europa Universalis IV or V) and tactics (‘win the battle’), asking the player to think about how they can win the battles in a way that wins the war.

Modeling Operations in WWII

All of this is somewhat difficult to describe but with luck some of the screenshots here have helped demonstrate, for those who haven’t played the game, how this system works.

There’s one final set of interacting mechanics here that we need to note which tend to govern the tempo of operations in Hearts of Iron IV: entrenchment and planning. Units that stop moving gain ‘entrenchment‘ over time in their current location, which provides a percentage boost to the damage they deal (‘attack,’ both ‘soft’ and ‘hard’ – we’ll get into this later) and reduces the damage they take when defending (‘defense’). In short, units that sit still in a province get better at defending that province, up to a cap. Full entrenchment is generally a pretty significant bonus and it can be very hard to move a group of well-entrenched infantry divisions off of a province with good defensive terrain (usually terrain with penalizes armor).

Planning works almost exactly like entrenchment except for attacking rather than defending. units assigned to an offensive plan (see below) and set up on the front line gain a planning bonus day by day which increases their attack and reduces they damage they take when attacking (‘breakthrough’). Whereas entrenchment instantly drops to zero once a unit moves, the planning bonus degrades slowly once a unit begins attacking and advancing.

In practice the interaction is this: at the start of an operation, both armies are likely already fully entrenched. To offset that substantial bonus to the defender (which the attacker cannot use – you do not get your entrenchment bonus when you attack, indeed attacking at all instantly sets a division’s entrenchment to zero), the attacker needs to build up a planning bonus, which typically might take something like two weeks of in game time (plus or minus various bonuses). Once that bonus is built up, the attacker strikes, using the planning bonus to overcome the defender’s entrenchment. If both sides are pure infantry, this may still not be enough, because infantry is much better at defending than attacking (high ‘defense’ but terrible ‘breakthrough’) but armor and airpower can tip the scales in favor of the attacker.

That said, once the defender is thrown off of their initial positions he loses his entrenchment bonus, while the attacker’s planning bonus is only slowly wearing off. The advantage thus swings to the attacker who has created a breakthrough, allowing them to widen gaps and push through to exploit the breakthrough. That said, soon enough the attacker’s planning bonus wears off and the constant attacking and advancing wears down the attackers organization (and equipment/manpower), leading the balance to shift back to the defender, who then re-entrenches, re-calcifying the lines in a new position. At which point the attacker, if they want to remain on the offensive, has to pick a new spot, set a new plan, resupply and reinforce their divisions, rev up their planning bonus again and then take another ‘punch.’

The result of this system is to create discrete, identifiable operations (the game will even name them for you). Players (and the AI) plan around these discrete smaller units of warfare with smaller objectives that occur on an observable rhythm.

And as a model of operations in World War II, Hearts of Iron IV broadly succeeds. There is enough detail in the resource and logistics simulation to model why offensives were mounted in the places why were and in the way that they were. The logistics and resource systems create objectives for operations that broadly match those attempted historically and the logistics system is also detailed enough to create the severe logistics hurdles that limited historical operations as well. Playing Britain, for instance, one quickly becomes familiar with the logistics problem in western Egypt and eastern Libya where the lack of infrastructure and rail lines means that as each army pushes forward from its supply bases, it becomes dramatically weaker, which can lead to the same kind of see-saw pattern, for the same reasons, as occurred historically.

Likewise, the system tends to push players towards doctrinal approaches that were successful historically, more or less. We’ll come back to doctrine in a bit, but players quickly discover that while broad linear offensives (using mostly infantry) can work, the more effective approach is finding points on which a lot of very mobile divisions (especially armor) can be focused to create a breakthrough (generally supported by air power), which can enable larger forces to be encircled or have their logistics unmoored. While the game somewhat struggles (as we’ll discuss) to really distinguish between the German and Soviet schools of thought as to maneuver warfare, this nevertheless is maneuver warfare and the game mechanics push the player towards that historical solution.

Meanwhile, the regular cycle of entrechment, planning, reconstitution and then planning again simulates the logistical and organizational complications that led to the operational tempo during the war. No one was, after all, attacking everywhere all of the time. Instead we can identify clear offensive ‘pushes’ which required both planning (in that coordinating so many troops and machines required advanced plans) and preparation (in stockpiling the troops, munitions and fuel) which took time. So, for instance, we can identify key major Soviet offensive operations on the Eastern Front: the winter counter-offensive (Dec 1941-May 1942), the failed Kharkov offensive (May, 1942), operations Uranus (encircling Stalingrad) and Mars (Nov 1942), the Soviet Kursk counter-offensive (July, 1943) and so on.¹¹

Indeed, the Hearts of Iron series remains extremely popular precisely because it so effectively models the operational level of World War II. This is hardly to say it does so perfectly – no game is going to fully capture the complexity of such a large war – but it does so better than any of its competition.

That doesn’t necessarily make it the ‘ultimate operational simulator’ however. Hearts of Iron IV is built to represent large-scale, division-level operations in World War II. As we’ll get to in later parts of this series, it really struggles to represent other aspects of operations: occupation, administration, dealing with partisans and other ‘unconventional’ warfare and so on. Notably, those systems are ‘split off’ from the core operational system, even more so than in previous Hearts of Iron titles. It was possible, for instance, in Hearts of Iron III to ‘spawn’ partisan units behind enemy lines during an offensive to represent coordination with resistance forces (as with the D-Day landings, for instance), but not in HoI4. The game has relatively little way of simulating, for instance, the way incessant partisan activity behind German lines made it difficult for reserve forces to move quickly enough to contain the Soviet breakout around Stalingrad during Operation Uranus (Nov. 1942) which resulted in the encirclement of Friedrich Paulus’ 6th army (along with elements of several other German armies) in a pocket around the city of Stalingrad.

It likewise struggles a bit to represent some of the fighting in the Pacific Theater where operations were often smaller than a division. The Battle of the Tenaru (Aug 21, 1942), for instance, was a significant allied victory that had a meaningful impact on allied (particularly American) morale in the Pacific, but as an engagement between two regiments (the US 1st Marine Regiment and part of the Japanese 28th Infantry Regiment) it lives entirely below the simulation level of Hearts of Iron IV. A player in HoI4 cannot send a regiment – much less a detachment of one – to Gaudalcanal. They must send a whole division or nothing – but for much of the early fighting on Gaudalcanal, neither side was at divisional strength.

Nevertheless, on the whole, the system succeeds. Of course the challenge it creates from a game design perspective is that it is very complex. Compared to a game of Europa Universalis V, where even a quite large empire might split most of its army into perhaps at most 6 or 7 ‘stacks,’ the number of maneuver units in HoI4 is overwhelming. To draw from my screenshots above, in my latest run, my British army in France and the Low Countries in 1939 numbered some 57 divisions and that is, by HoI4 standards, a relatively small army for a major country. For many players, controlling such a large army might be bewildering or alternately frustrating in its granular detail.

Which brings us to:

Fronts, Armies and AI Generals

Attentive eyes on the screenshots I have been using here (and will keep using) may note that sometimes the map has these wonderful drawn front lines and operational arrows and sometimes it doesn’t.

That is because one of the innovations of Hearts of Iron IV was the decision to include a system for automating the operations we’ve been describing. In the past I’ve talked about ‘generations’ of Paradox titles, distinguishing between the very ‘on rails’ second generation Paradox titles (HoI3, Eu3, Victoria II) and the more simulationist, free-form third generation titles (EU4, Crusader Kings II and III, Imperator). I wonder if the trend that won’t end up defining a ‘fourth generation’ of Paradox’ games isn’t the effort to enable a greater degree of accessibility – a broader audience – by allowing players to simply automate entire systems of the game to a greater or lesser degree. You see a bit of this in Victoria III and a lot of it in Europa Universalis IV (where nearly every system can be turned over to AI control), but Hearts of Iron IV, despite falling firmly within the third generation chronologically, shows some of the earliest experimentation with this kind of automation with what I am going to call its ‘war plans system’ which has been part of the game since its launch but was absent in its predecessor, HoI3.

The first part of this system is the highly simplified HoI4 order-of-battle system. Whereas Hearts of Iron III had a fairly complex order of battle system: brigades were grouped into divisions (unlike in HoI4, in III, brigades could be freely moved between divisions or deployed independently), which were grouped into corps, which were grouped into armies, which were combined into army groups, which were assigned to a theater, which each level having its own commander and a command ‘range’ in which their bonuses would apply. Each level above the division also had an HQ unit, representing where the commander and his staff were.

HoI4 radically simplified this: divisions became effectively ‘atomic’ units – unable to be divided into their components – and they are grouped directly into armies (no corps). Each army can have around 25 divisions in it and has one commanding officer, who can have an HQ on the map, but does not need to. An Army Group, in turn, can combine up to five armies. As noted above, these are not ‘stacks’ – the divisions continue to move independently. While HoI4 has ‘theaters,’ these are mostly player-UI elements, they do not provide command bonuses. HoI4 thus compressed HoI3‘s six-level org chart into just three: divisions, armies, army-groups.

However, HoI4 added automation to those armies: you can assign an army a stretch of frontline and the AI (representing the army commander) will automatically deploy the army’s divisions to defend that front line. The player can then draw an offensive line on the map, indicating where he would like an offensive to end up if successful, which creates a war plan at which point divisions begin to accrue their planning bonuses (above). The player can then, at any time, order the army to execute the plan and it will begin attempting to push to the intended ‘finish’ line, taking provinces in sequence (with some attention given to frontage and using easier-to-take provinces to lever enemies off of harder ones) until it gets there or the player orders a halt. It is also possible, though this system, to order amphibious or airborne operations (and indeed, unlike land-based offensives, they can be conducted no other way).

It is thus possible in HoI4 for the player, rather than micro-managing every division, to instead place their armies on the front line and draw arrows where they want them to go and then for the most part let the AI (again, simulating those army and army group generals) ‘figure out’ how to get there, akin to the way that the leader of a country or a high command (like the Soviet Stavka or German OKW) would determine general objectives and then let generals ‘on the ground’ come up with the detailed plans on how to reach them. AI controlled countries use this system exclusively to conduct their warfare.

And it is easy to see the intent here and how it aligns with the historical vision of the game. After all, the player in Hearts of Iron IV is not a corps commander, they are directing the entire military – land, air and naval assets, industrial production, doctrine and even policy – of a country. You play as the state (and continue to do so even if the government of the state changes; we’ll come back to that), after all. So instead the idea is that the player merely draws the war plans and determined the composition of the armies that will execute each part of the plan (indicated by its own frontline and offensive lines) and then, when the time is right, triggers the plans and lets the simulation handle the messy details of coordinating attacks.

However, whereas Victoria III (which has a similar ‘automated’ war system) forces the player to use it and does not offer the option for manual control, Hearts of Iron IV keeps the ability for players to move divisions manually. My suspicion is that most plays rely on a mix of automation and manual direction, though my impression is that I use rather more manual direction than most, a product of having been playing the series since Hearts of Iron II (where no automation option existed). It is not possible to build a planning bonus without a war plan, with the result that even when I am planning to entirely manually control an offensive (which I usually do), I will begin by drawing an offensive war plan somewhere (it does not matter at all if the arrow is pointing where I intend to go) in order to build that planning bonus. But I’ll then commence the attack by deleting the war plan so the AI doesn’t shift divisions around without my say so.

There are advantages to manual deployment in this way, which mostly gets down to precision control. The army AI has gotten a lot better over the years, but on the defensive it still tends to shift divisions around too much and doesn’t defend in depth effectively. The latter matters a lot because if you are expecting to get pushed from a position, it is a good idea to have divisions already place done province back so that they have their full entrenchment bonus when the enemy tries to breakthrough. Likewise, shifting divisions around a front removes their entrenchment bonus, which can be disastrous if done at the wrong time.

On the offensive, the army AI is reasonable competent but broadly speaking a bit wasteful compared to a player, far more willing to launch attacks that have little chance of succeeding because they’re ‘part of the plan.’ Consequently when doing large-scale offensives I often leave my leg infantry under AI control on front lines (but without any attack orders) while micro-managing my armored, mechanized and motorized divisions (which are doing most of the attacking): the result is that as I push forward, the front lines automatically adjust, causing my leg infantry divisions to file into and dig in into new positions as the armor advances.

Most of the Game

What I think is most significant, however, for Hearts of Iron IV‘s view of history is simply that the operational-level simulation is most of the game. Whereas Victoria III completely automates its front lines because warfare is less important compared to politics and economics in that game, Hearts of Iron IV provides automation tools because it invests so much player attention into the operational level of the game that it becomes simply overwhelming.

It is difficult to measure just how much Hearts of Iron IV is a game about the operational – rather than strategic – but the playtime balance in any given ‘run’ between pre-war and war is instructive, because the strategic layer (political focuses, industry management, research, espionage) work at the same speed both pre-war and during the war, but the operational element becomes massively more complex once the shooting starts. In my current UK run, I covered the three years from game start in 1936 to the beginning of the war in 1939 in a single play-session that lasted about four hours (including a break for dinner!). Making it to 1944 (where I am now as I write this) by contrast, took a dozen play sessions over two weeks that took up more than 20 hours.

So while I cannot speak for the ‘typical player,’ I would suggest we might place the balance that in a typical run (which usually ends in ’44 or ’45 – few players push past the end of the war and there is almost no content there to play anyway), a player might spend something on the order of three-quarters of their time and attention entirely on the operational level (including naval and air warfare), with the remaining one quarter split over politics, industry, research, espionage and so on.

And that gets us to perhaps the most important part of Hearts of Iron IV‘s theory of history: in Hearts of Iron IV, ‘history’ is mostly a history of warfare fought on the operational level between conventional armies with division-sized elements. That is, to be clear, not an absurd way to frame a game about World War II. World War II was a lot of other things too, of course – it was an enormous and incomprehensibly complex conflict – but in terms of setting a game’s focus, it makes sense.

However, it is important to note everything that gets neglected in that focus. Small unit actions are left out, partisan activity is barely simulated, war crimes are entirely removed (we’ll get to it), asymmetrical warfare – often an important part of WWII – is mostly absent as is the experience of war. We’ll see this even more as we begin to look at other systems but Hearts of Iron IV has almost nothing to say about the experience of World War II; the comparison with Crusader Kings or Victoria, which have a lot to say about the experience of the Middle Ages or industrialization is really marked. The game never asks you to consider the experience of being an individual soldier or worker during these events and it – for reasons we’ll get to – really never asks you to consider the experience of being a civilian caught in the maelstrom of atrocity and violence. It doesn’t even have much to say about the experience of being, say, Sir Claude Auchinleck, sweltering in the heat of North Africa trying to coordinate an offensive and make sense of confusing information while managing (or, in the event, failing to manage) the expectations of Winston Churchill.¹²

Hearts of Iron IV is the most popular Paradox title, by a country mile. It is quite possibly the most popular current strategy game on the market. Its influence is significant enough to be detectable in the patterns of political thinking that show up in both commentary and decision making. And yet it is, by far, the narrowest Paradox game, with the thinnest vision of history. Again, that is not necessarily a critique – it is fine to make a game about operations. But Hearts of Iron IV is fundamentally a game about operations in WWII, rather than a game about WWII.

Next week, we’ll start diving into the systems that create the ‘shell’ around Hearts of Iron IV‘s impressive operational simulator and I am going to start to have a lot more unkind things to say.

1. You know, initially when I wrote this, I included the Tennessee Williams reference because I like the phrasing and was going to put in a footnote saying that it didn’t really have any historical content here, but I am checking and The Glass Menagerie premiered in 1944, so it is actually historically on point. Neat!
2. While Crusader Kings III and Stellaris have posted similar ‘peak’ numbers (typically early after release or a major update) to HoI4, on any given day there are usually as many people playing HoI4 as there are playing CK3, Stellaris, and Victoria III combined. As I write this sentence, there are (according to SteamDB) about 50,000 people playing HoI4 on Steam, compared to 22k for CKIII, 12k for Stellaris, 11k and 9k for EU4 and EU5 respectively and roughly 8k playing Victoria III. This is despite the fact that HoI4 has not had a recent update in the past few months.
3. I am going by Steam stats but the strategy genre remains so PC-dominated that – unlike many other genres – I think this is basically a fair way to estimate total player counts. I think it is plausible that non-steam player numbers bring Sid Meier’s Civilization VI roughly to parity with Hearts of Iron IV, but that is the only real competition here.
4. Interesting, I’d argue more so than its successor, EUV
5. For what it is worth, I find the idea of ‘operations’ as a third category between tactics and strategy is just a fantastically valuable teaching tool for students just beginning to grapple with the nature of war that it is very hard to ever fully abandon the ‘operational level’ as a classroom idea, even if it is perhaps something that a mature practitioner is going to ‘complicated out of existence.’
6. To be clear, a skilled player in CKIII or EU5 absolutely can tilt the outcome of battles in their favor through canny maneuvering before contact, but there is a real difference here both in granularity (how many decision-points you get) and level of impact.
7. One of the great advantages of faster divisions (cavalry, but really motorized or mechanized infantry and armor) is that they can move quickly enough to attack retreating divisions before they reorganize, allowing them to ‘keep a beat enemy beat’ as it were (and potentially overrunning them).
8. My own, somewhat vulgar, pet term for abusing the frontage rules is a ‘width screw,’ (since the HoI series has used ‘frontage’ and ‘combat width’ somewhat interchangeably) which comes in two forms: either expanding the combat width way more than the defender has divisions (so you have several divisions beating on just one or two) or alternately shrinking the combat width way less than the defender has divisions (so that most of his divisions are stuck in reserve, unable to move or regenerate, but not actively fighting). The former, of course, simulates a force being flanked, the latter is the best way to accomplish a ‘spoiling attack.’
9. Though the AI will calmly sit in low supply and attrition rather than abandon a front line that cannot be held. Players, by contrast, can just evacuate untenable salients.
10. It can also create huge gaps in the enemy line which can be exploited: if their old front line is in the bag, then you have a window of opportunity to rush through the hole created behind them.
11. Indeed, one of the things that Jonathan Parshall notes contributed to early Soviet offensive failures in 1942 was that Stalin did not allow for enough time to plan and prepare, instead insisting on immediate offensive action. By late 1942, he seems to have recognized the folly of this and Soviet operations become more deliberate and less rushed, leading – alongside improved equipment, doctrine and a host of other factors – to more effective operations and eventual Soviet victory.
12. I give this sort of example because this is exactly the experience that CKIII is interested in, “what is is like to be a leader in this place at this time?”