EU4 Army Compositions - How does combat really work in (2024)

EU4 Army Compositions - How does combat really work in (1)

Europa Universalis IV is a game about numbers… lots of numbers and how they interact with lots of other numbers. As a result, nothing is ever as simple or one sided as it might appear, which is one reason the game has so much re-playability. If you’ve been playing for a while you’re likely to have stumbled onto your favourite builds and army compositions, but are they optimal?

There’s a lot to talk about when it comes to your armies and we’ll do our best to cover most of it here, sharing what we’ve found from playing the game and what others have contributed to the endless discussion.

EU4 Army Compositions - How does combat really work in (2)

<h2<The Basics</h2>

Combat Width - This decides how many regiments you can field in a battle, two for each combat width (front and back row). This number starts low and increases as your technology progresses. You should aim to have enough units to fill at least one row where possible, with any artillery being on top of this.

Unit Pips - When it comes to choosing which unit to field, pips matter. During each combat phase offensive pips increase damage dealt, and defensive pips decrease damage taken. After artillery becomes available, defensive pips become more valuable as they effect both lines. Morale pips should take top priority here as they are used in both combat phases.

Deployment - In simple terms, the front row will fill with infantry with a small number of cavalry to the sides. Artillery will be positioned in the back row unless they outnumber the infantry and cavalry, in which case they will even out the rows by adding some to the front. Any space left over in the second row will fill first with infantry then cavalry. Any excess units are added to the reserve.

Phases - Each combat phase lasts three days and alternates between Fire and Shock and both sides roll a die at the beginning of each. This is combined with any other modifiers (leader/terrain/unit pips) but cannot equal less than zero. Each day of a combat phase, the game calculates kills and morale loss.

Targeting - Normally units engage enemies directly in front of them but they can attack any unit within their flanking range if doing so will result in greater damage to the enemies combat ability. Artillery can fire from the back row but only do 50% of their potential damage from there.

Morale - Units take morale damage for every day in combat (including reserves), with greater loss for receiving actual damage. Once it hits zero, the army attempts to retreat. At this point, two more fire and shock phases are played out and if the retreating army has zero morale and is outnumbered 2:1 before those are completed it is destroyed in a stack wipe. As this is such a critical stat, efforts should be made to increase morale where possible.

Discipline - An often forgotten stat with only limited small modifiers it is nonetheless important. Damage dealt is multiplied by your discipline, and damage taken can go up or down depending on the percentage.

Supply Limit All provinces have a supply limit based on the terrain, development, and various modifiers. As an example, an army leader with 2 pips in manoeuvre will increase this limit by 2 for their army. As a guideline you will get the biggest positive modifiers on coastal zones, then as the owner of a province, then with allied/access/controlled provinces, though the biggest bonuses come from military technology levels.

Attrition - If the army size of all non-hostile armies is above the province Supply Limit at the beginning of the month, they will take attrition damage. Attrition damage is capped at 5% maximum, but scales depending on how much you are above the limit and what the limit is. For a simple example, in a 40 supply province, you would suffer 0.25% attrition (10 divided by the supply) for each point you exceed the limit by, so going over by 4 units would lose you 1% per month. A modifier that reduce attrition by 25% would reduce this to 0.7% (multiplicatively maths, just go with it), while also capping the attrition at around 4%. Sieging a province adds 1% attrition no matter what, which would increase our example to 2% - it all adds up.

Reinforcements - This is how fast you can pull men from your manpower pool and have them join your weakened armies. There is a massive monthly ducat cost to reinforcing armies so speed modifiers can save you a lot of money. This cost only applies if your army is below max strength, so when dealing with attrition, if you can send enough men to cover the losses there is no additional cost. That said, attrition can rapidly deplete your manpower through stealthy reinforcement, so keep an eye on it closely.

Attack and Defence - The defender almost always gets an advantage in battle, so luring the enemy to you, or tackling them while they are sieging your provinces (which counts as defence) is the best bet.

Terrain - Terrain penalties can be harsh on attacking forces, so where possible avoid mountains, hills, and woodlands if you really must engage. Mountains give -2 to the attackers dice roll, essentially cancelling out early game generals. Hills and woodlands are only -1 but these modifiers effect both combat phases so best to avoid.

Crossings/Landings - Same as the terrain really. Straits and naval landings give -2, and rivers -1. In the case of multiple attacks from different directions, the worst modifier is used for the whole attacking force. If the attacking leader has higher manoeuvre than the defender, this penalty is negated, so high manoeuvre pips are excellent for attacking armies.

Professionalism and Drilling - Both provide insane bonuses to your army strength at 100%. Professionalism can net you 20% to siege ability and 10% to combat damage in both phases. Various milestones also unlock abilities like Supply Depot that can massively increase your supply limit in an army location and will let you play with bigger stacks. Drilling has even better numbers but no milestones. It’s also tied directly to a single army but having another 10% to damage dealt, and a staggering 25% reduction to damage received makes drilling a no-brainer whenever you have the option.

Army Tradition - Grants morale and manpower bonuses but you’ll often get hit with events and natural decay to counter it getting really big. Great if you can be bothered with it and the morale boost really helps winning those otherwise equal battles.

Other Modifiers - There are too many modifiers to go into here, but stacking them up pretty much works the same regardless of your choices. Pick what suits your playstyle but if you’re looking for the perfect army, focus on the military ideas and don’t forget to synergise with policies for some too big to believe bonuses.

EU4 Army Compositions - How does combat really work in (3)

Unit Types

Infantry - The grunts of any army composition, they deal the damage and take the hits, suffering the highest casualty rates. They are the cheapest unit and you always need them. As mentioned above, once artillery comes into play, pick morale and defensive pips.

Cavalry - The flankers that sit on the ends of the front line. They will fill spaces in the back but only after artillery and infantry have run out. Quite expensive for what they are and only really useful if you have a greater combat width than your opponent or you’re tackling armies that don’t fill out their own front lines. They become increasingly redundant as the game goes on but you can’t really go wrong with a handful in each stack. If you’re facing smaller armies where you can make good use of flanking bonuses, offensive pips are useful here.

Artillery - The big guns. They are the only unit that can fire from the back, although they do so with a 50% damage reduction. Either way, being on the back line means they won’t take damage until they are forced to the front by loss of infantry. Very expensive to buy and maintain being three times the cost of infantry. At later levels, there’s no choice for artillery but what you’re given, so pips don’t matter much.

EU4 Army Compositions - How does combat really work in (4)

Army Composition

The optimal composition is talked about a lot and in many ways it is set in stone, and while we’ll go over it and why it’s so good, we’ll also look at why it isn’t always what you want.

For that perfect storm of battle prowess, you want to be aiming to fill the entire back line with artillery and the majority of the front with infantry, leaving perhaps two spots free for cavalry. There are also variations based on what stage of the game you’re in, but for the majority of the game - and in the common vernacular - you’re looking at a 10/2/12 ratio, scaling to your combat width and replacing excess cavalry with more infantry. This ratio will give the army the single greatest opportunity to win an army of that size would get, everything being equal.

The problem with this comes from many of the things we talked about earlier, firstly the damage suffered by infantry. If you lose 4 units from a 12 length line, 2 of the cannons move forward to even out the formation, exposing them to fire.

You can counter this somewhat by adding more infantry to the composition, but this usually involves hitting supply issues. Let’s take an reasonable mid-game enemy province giving you a supply limit of around 30. At that point in the game you’ll likely have military technology giving you a line width of 30 as well. Even following the basic ratio, you’re going to want to fight with a total of 60 regiments (not counting reserves). Given a general with 3 manoeuvre pips, you’re still 27 over the limit. Using the maths we talked about earlier (10/30=0.33)x27=9 we get the maximum attrition (5% or 4% with defensive ideas). 5% of 60,000 men is 3,000 casualties every single month. Over a 12 month campaign, that’s 36,000 dead from attrition alone, in each army.

Split stacks I hear you say? Well yes, we can do that, but if you’re splitting your stacks, you’re also halving the artillery that can be deployed. If you’re wanting to maintain a full front line or have infantry reserves for your merged army you’ll probably end up with a full 30 infantry/cavalry and 15 artillery in each smaller stack. You’re still looking at an army stack of around 45, while sacrificing artillery support if you fight alone.

But would you fight alone? Probably yes, it happens… but isn’t the point of splitting stacks to avoid attrition until you can begin a battle - when attrition is placed on hold - and pile them back into one? Yes, but you’ll also be using smaller stacks to siege and chase down smaller forces, and sometimes they can get cornered.

From this we can already see the magic ratio is broken. We know the optimal battle composition, but we’ve learnt that it fails in terms of war composition. Even split stacks will often face issues with supply. So the test is figuring out what you can get away with at the time. We take the average supply you’ll be facing in a given conflict (how big your armies should be to avoid taking the heaviest penalties), how many stacks you intend to merge for a fight, and how they will cope fighting alone.

You usually want to max your front line, so whatever that number is make sure you have enough infantry and cavalry to fill it out. In our example that’s 30. If we had split the stack as before it would be hitting 45 with artillery and taking pretty hefty attrition in a 30 supply province (pretty much the full 5%). If we lower the artillery to just 10 though, it drops attrition to 3.3%. With these army sizes that lowers your 12 month loss from 27,000 men, to only 15,840. Okay, so that’s still a lot but it’s a lot better than before, and all for dropping only 5 units. 10 artillery is also the prime number for mid-game siege bonuses (although the bonus is based on per thousand men not the number of units, so any casualties that aren’t reinforced will reduce your siege capability).

You could further reduce this attrition by decreasing your infantry numbers below the combat width, but that becomes increasingly dangerous if that army is ever confronted alone where it will face flanking penalties. If you do go this method, remember as well that though you may start out with enough reserves once the armies join together, over the course of a war you may find reinforcement can’t keep up with your losses which means it pays to have extra infantry around anyway.

Even so, we’re now talking about having only 10 artillery included, the perfect sieging stack for mid-game or lower level forts later on, and reasonably sized to avoid the worst of attrition. With only a third of our combat width in artillery though, we’ll want to be merging 3 armies for any battle, which is definitely doable, if a little awkward when dealing with enemy zones of control. Does this mean we now have too many infantry? This depends on how much you intend to use them solo, and remember, the larger the stack, the lower the chance of getting wiped.

Does this make it the ideal composition? Another loaded question as it all varies on your circ*mstances, as having lots of manpower could offset your attrition losses but lets look at it from one final angle - the economics of war.

EU4 Army Compositions - How does combat really work in (5)

Economics of War

As with supply, money is limited. Ducats are needed to finance everything from buildings to your military campaigns. Every ducat a month you spend on a unit is one less you have to invest during peacetime. You can slide the Army Maintenance way down to save a bundle when you don’t need them, but you should always be drilling your forces to full, so you can’t really cut maintenance if you want to maintain an optimal army.

Artillery costs three times more than infantry to buy and maintain, so if you’re struggling for money but have some spare force limit, padding your armies with infantry makes even more sense. As infantry also take the most damage in wars, you can use extras to artificially increase your manpower pool by consolidating them directly into wounded units rather than drawing from reinforcements. With this you can get great value for money.

EU4 Army Compositions - How does combat really work in (6)


To wrap it up, we’ve seen there is a perfect composition and a best unit to pick from each type to give you the greatest chance of winning a battle, but in practice tying yourself to that will often cause more trouble than it’s worth. Best bet is to ensure that your merged armies will have enough artillery to fill the back line and whatever number of splits you make are able to minimise their attrition while still being able to fight alone if they have to.

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EU4 Army Compositions - How does combat really work in (2024)


How does eu4 combat work? ›

Combat is divided into a series of 3-day phases. Phases alternate between Fire and Shock, with the Fire phase happening first. At the beginning of each phase, each side rolls a die. The result is used to determine the morale damage and casualties inflicted to the opponents each day in the three-day-phase.

What is optimal eu4 army composition? ›

Ideal army composition for every tech

6 24 26 4 0 30 Also, if you have insane cavalry combat ability (eg. Poland) you can consider adding more cavalry. 9 25 27 4 0 31 If you have any sense of army aesthetics, add one inf to odd numbers for when you split the army up to avoid attrition.

What is the use of cavalry in eu4? ›

Cavalry is good for flanking once the main line has been filled, but are much more expensive than infantry. All cavalry have 2 pips in maneuver. Cavalry costs 2.5 times as much as infantry. They are more powerful than infantry, especially during the shock phase of combat.

How does the army work in EU4? ›

The basic unit of land forces is the regiment, each consisting of 1000 soldiers at full strength. Each regiment is classed as Infantry, Cavalry or Artillery. Regiments are grouped into armies. Each army can be led by a general or conquistador.

Is eu4 realistic? ›

EUIV being a sandbox game is as accurate as it can be at the start of the game. However, as you continue with the game further into the timeline a divergence can occur from a historical accuracy standpoint.

What is the end goal of eu4? ›

The game is a sandbox environment; while there is no strict rule on winning the game, the game of the player is over when the player's nation is removed, or annexed, from the map or the date reaches the year 1821.

Who has the best army in eu4? ›

That said, Poland is still by far the strongest military if well built up, even completely ignoring hussars. There's 0 competition here too.

How to make a strong army in EU4? ›

For buffing your armies, morale and discipline are the main factors. Early game morale is more important. The higher your morale is the longer your army will be able to keep fighting, if you outlast their army then yours wins. Early game morale is pretty low all around, so bonuses to it count for more.

What is the max war score in eu4? ›

The scale ranges from +100% (a complete victory for the side currently being viewed) to −100% (complete defeat for the side currently being viewed). Warscore is measured using a number of different parameters: Occupied provinces. Battles won or lost, to a maximum of 40% in either direction.

Why is cavalry so strong? ›

Cavalry had the advantage of improved mobility, and a soldier fighting from horseback also had the advantages of greater height, speed, and inertial mass over an opponent on foot. Another element of horse mounted warfare is the psychological impact a mounted soldier can inflict on an opponent.

What unit is best against cavalry? ›

On narrow maps with lots of obstacles like cliffs or woods, cavalry units can fall prey to ranged units that can exploit their range. Camel Riders, Mamelukes, Flaming Camels, Kamayuks, and Genoese Crossbowmen also have bonus attack against cavalry units.

Which unit is strong against cavalry? ›

Infantry blocks cavalry charges; Infantry has an advantage over Cavalry, Archers shoot infantry; Archers have an advantage over Infantry, and Cavalry is so fast that they are so difficult to hit, that they are able to charge and reach archers.

What do forts do in EU4? ›

Forts limit unit movement due to their zones of control ("ZoC"). This article explains precisely how they used to work in version 1.28. The key concept to understand is that movement of a unit depends on what its "Return Province" is, and not just on the province it is or the adjacent province it came from.

What is the calvary to infantry ratio EU4? ›

The base ratio is 50 percent, so an army with 22 units of infantry shouldn't have more than 11 units of cavalry.

What is the force limit in EU4? ›

A force limit is a soft limit on how many ships or regiments a country can possess. It can be exceeded at a monetary price.

How is the war score calculated in eu4? ›

Warscore is measured using a number of different parameters: Occupied provinces. Battles won or lost, to a maximum of 40% in either direction. Blockaded ports.

How to make a strong army in eu4? ›

For buffing your armies, morale and discipline are the main factors. Early game morale is more important. The higher your morale is the longer your army will be able to keep fighting, if you outlast their army then yours wins. Early game morale is pretty low all around, so bonuses to it count for more.

How do Crusades work in eu4? ›

Crusades are to give bonuses to you plus whatever allies you call in and for helping countries who are already at war with target or who will soon be. It won't make countries that would never declare war on the target do so but it will make countries that were already itching to do so the final push to.

How to defend colonies in eu4? ›

As grotaclas said you can use Enforce Peace to come in to protect your colonies. You can also set your message settings to warn you and pause the game whenever someone declares war on your subjects. Keep a moderately sized army in the New World and all those native attacks become free real estate for you.


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