Welcome to the EU4 War Academy! In this detailed guide, we break down the often misunderstood but critically important military mechanics in Europa Universalis IV. From combat phases and damage equations to late-game artillery tactics, this article distills everything you need to know to build optimal armies at every stage of your campaign. Whether you’re facing early tribal skirmishes or late-game mega-wars, the insights here will give you a strategic edge on the battlefield.
The Basics of Combat: Fire, Shock, and Dice Rolls
Every EU4 battle is a dance of three-day phases alternating between Fire and Shock. Fire comes first, representing ranged weapons like muskets and cannons, while shock reflects hand-to-hand combat like pikes and sabres. This cyclical rhythm continues until one side is completely routed.
Damage is calculated through a complex equation with many variables, but at its core is a base formula: 15 × regiment strength. That means on the first day, a full-strength regiment inflicts 15 casualties. As troops die, damage output drops proportionally—dead men don’t shoot.
Then dice rolls kick in. Each side rolls a number between 0 and 9, multiplied by 5 and added to the damage. A lucky roll can swing a battle, but it’s random, so don’t base your strategy around it. Instead, understand how to stack modifiers in your favor.
Leadership, Terrain, and Unit Pips
General pips in Fire and Shock modify rolls. If your general has more pips than the enemy’s, you get a bonus equal to the difference. It’s a simple but powerful advantage.
Terrain also influences combat. Attacking into woods, hills, or marshes applies a -1 penalty; mountains hit you with -2. Always check who’s considered the attacker—sieging armies are always the attacker, regardless of who initiated combat. This makes mountainous forts particularly valuable.
Unit pips, just like generals, add offensive or defensive bonuses based on the phase. Offensive pips increase your roll; defensive pips reduce incoming damage. These are built into each unit type and can make a difference, especially early on.
Understanding Flanking and Combat Width
In a real war, your regiments don’t fight one-on-one. They line up across a battlefield based on combat width, which increases with military technology. The flanking range of units determines how many slots to the side a unit can hit. Infantry start with a flanking range of 1, while cavalry start with 2.
But here’s a twist: just having more troops doesn’t guarantee more damage. If you stack 20 units against 5 enemies, the extra units beyond the flanking range just stand there.
That’s where cavalry come in. Their extra flanking range lets them reach and damage side units infantry can’t. But be warned—EU4’s automatic deployment isn’t perfect. If you only bring two cavalry, the game might place them suboptimally. That’s why, despite some theorycrafting, the most reliable early army is lots of infantry and four cavalry. That avoids misdeployment and maximizes your early effectiveness.
Exceptions exist. If you’re a horde or have major cavalry bonuses, build more cavalry. Otherwise, keep it minimal.
The Late Game: Cannons Take Center Stage
Once you hit military tech 16, the battlefield changes dramatically. Wars scale up, multiple stacks get involved, and artillery becomes the dominant force.
Artillery has two defining traits:
- It attacks from the second line at 50% damage, which still significantly boosts your overall kills.
- It takes double damage if ever exposed in the frontline.
So rule number one: never let your cannons touch the front line. They only survive and shine when shielded by infantry.
That brings us to optimal late-game composition. You need to fill both your frontline and backline according to combat width. If combat width is 30, build 30 infantry and 30 artillery. That’s the basic gold standard.
What about cavalry? By this point, it’s obsolete for most nations. Its flanking advantage disappears when battle lines are full, and it becomes an inefficient drain. Unless you’re Poland or extremely cavalry-boosted, drop cavalry entirely in the late game.
Infantry Strategies: Three Schools of Thought
Now comes a nuanced decision: how many infantry should you bring beyond the core line?
1. Symmetrical Stacks (30 infantry, 30 artillery)
- Best for siege-heavy or dominant positions.
- Minimizes attrition.
- Worst for durability. Once infantry die, artillery gets shredded.
2. Infantry Reinforcement Stacks
- Keep 30/30 battle stacks, and reinforce with separate pure infantry armies.
- Efficient and sustainable.
- Vulnerable to AI maneuvering if infantry stacks get caught.
3. Hybrid Stacks (extra infantry in core stack)
- Add 10–50% more infantry to your main army.
- Versatile, durable, good for mid-to-high intensity wars.
- Slightly more attrition and less efficient, but avoids many pitfalls.
Pick based on your playstyle, nation economy, and enemy strength.
Final Tips: Managing Reinforcements and Attrition
Supply limits won’t let you walk around with 60-regiment doom stacks. Split your armies in half for movement. Bring them together for battle.
Ensure stacks arrive on the same day when reinforcing. If not, the combat system might weirdly deploy infantry in the back while cannons wait uselessly. Don’t give up free power.
Also, remember: artillery in the second line is doing work. Artillery in the front line is a catastrophe. Always monitor reinforcement ratios so infantry dies before cannons.
In Summary: Early vs. Late Game Army Templates
Early Game Composition:
- Infantry-heavy
- 4 cavalry (unless you have bonuses for more)
- Minimal artillery, if any
Late Game Composition:
- Infantry equal to or more than artillery
- 0 cavalry (in most cases)
- Artillery matching combat width
Understanding these systems won’t guarantee victory—but it will eliminate most avoidable mistakes. Many EU4 players lose not because they’re outmatched, but because they mismanage army structure. Let the AI waste manpower on awkward stacks—you’ll be the one with a reinforced line, optimized damage, and a long-game plan.
Stay tuned for the next installment of the War Academy, where we dive into modifiers like discipline, tactics, combat ability, and more.
Until then, may your front lines hold, and your cannons fire true.
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