EU5 Army Composition Explained

Building an army in EU5 isn't a question of "how much combat power can I stack" the way it often was in EU4. Four regiment categories each carry a different combat speed, flanking profile, and damage type, and the game's own terrain rules decide how many of them can actually fight in a given location at once. Get the mix wrong and you don't just lose a fight slower. You can lose to a smaller force that out-flanked you.

The four regiment categories

Infantry forms the largest share of most armies because it's cheap, holds ground, and doesn't leave a gap for the enemy to exploit. Cavalry moves faster and flanks harder (its 200% flanking ability against infantry's 100% is what makes cavalry-heavy armies feel so aggressive in the early game), but its 0% secure-flank rating means a cavalry unit that gets flanked itself takes that damage with no mitigation at all. Artillery can't meaningfully flank or be flanked in the open the way cavalry can; its real job is sieges, not field battles, and the wiki notes reinforcements draw manpower at five times their normal maintenance cost, so a heavily-attritted army is expensive to rebuild, not just slow to rebuild.

Combat width isn't a flat number

EU4 veterans looking for a single "combat width" number (the flat 40-width most late-game EU4 fights converged on) won't find one in EU5. The wiki instead ties it to terrain: "the maximum number of units that can be engaged at once in each section depends on the location's Possible Frontage and each unit's Frontage." Mountainous woods terrain loses six points of possible frontage total (−4 from mountains, −2 from woods) compared to open ground, so the same army that fights efficiently on a plain can find a meaningful fraction of its regiments locked out of a mountain battle entirely. Rivers apply a −1 penalty to the attacker's combat dice roll and straits apply −2, on top of the frontage loss. Crossing water to attack an entrenched defender is a real tax, not flavor text.

Why pure-cavalry stacks are strong now, and why that's changing in 1.4

Cavalry's current combination of high flanking ability and zero flank vulnerability trade-off (200% flanking out, 0% flank defense) makes cavalry-heavy compositions genuinely strong in the live 1.3.11 game, and it's the reason "just build cavalry" is common early-game advice in community threads. Paradox has already announced this is changing. Tinto Talks #118 (2026-07-29, on the official Steam news feed) states the developers are reducing "cavalry combat power from 4 to 3.25" for the 1.4 "Río Salado" patch specifically because pure-cavalry armies were dominating; the same post states cavalry was delivering "60% more combat per battle line slot than infantry" under the current numbers. Flanking effectiveness is also being cut in the same patch: the flanking bonus for light and heavy cavalry drops "from +110% and +100% down to +60%." The stated goal is to push players toward "infantry in the center with cavalry on the flanks," a combined-arms composition, rather than letting cavalry alone win fights.

The same dev diary announces two related changes worth knowing if you're planning a longer campaign around current numbers: siege artillery becomes more efficient (only 2 artillery regiments needed per point of bonus against forts, down from 3), and fort garrisons will auto-surrender once they fall below 5% of their maximum strength rather than the old system based on absolute defender counts. Both ship in the same 1.4 patch as the cavalry rebalance, per the same Tinto Talks post.

Building a composition that holds up under both

Given the current live stats, a composition that leans on infantry for the center and uses cavalry specifically for flank protection and pursuit, rather than as the bulk of the army, already performs better against a competent opponent than an all-cavalry stack, because an opponent who successfully flanks a cavalry-heavy army punishes that 0% secure-flank rating hard. That advice gets more true, not less, once the 1.4 changes land: a cavalry-power cut from 4 to 3.25 plus a flanking-bonus cut from +100-110% to +60% closes most of the gap that made pure-cavalry stacks dominant in the first place. Artillery earns its place for sieges specifically. Don't drag a full artillery train into a field battle where it can't secure its own flank, and do bring enough to hit the improved 2-regiments-per-bonus-point threshold once 1.4 ships.

Related reading

For the layer above unit composition, what government type and reforms actually change about the army you can field, see government types and laws explained. For a nation whose entire military identity is built around cavalry-and-infantry combined arms from the start, see the Ottomans strategy guide. For the full list of what's confirmed for 1.4 beyond combat, see upcoming patches and DLC.