Combat/Ground

Combat in Endless Space 2 is split into two parts: ship combat, taking place between fleets in orbit around systems, and ground combat, taking place between soldiers on a planet's surface. Both forms of combat are largely automated, but choices can be made at the start of combat that can have significant effects on the outcome.

Space
**Ground**

Ground Battles are fought on systems after a fleet deploys its manpower as part of an invasion. These battles can last multiple turns, during which the attacker and defender can choose different tactics. If they are victorious, the attacker gets to decide what to do to the system.

## Sieging

If a hostile fleet orbits an enemy system with no other enemy fleets distracting them, they automatically lay siege to the system, reducing the system's defensive manpower  every turn. While a system is sieged, it can't refill its , send or receive any civilian ships, or produce any strategic or luxury resources for the empire.

> ℹ️"Hostile" here means either the two empires are at War, or they're in Cold War with the besieger having the "Righteous Fury" Religious automatic law, or they're in Cold War with the defender's system being within the besieger's cultural boundary, or the defender is an always-hostile minor faction like Pirates.
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Larger ships, more weapon modules, or some support modules can increase the amount of  lost each turn.

The purpose of sieging is fivefold:

* It conserves your manpower.
* Done right, it let you conquer a system with minimal damage to what is about to become *your* system.
* To prevent enemies from producing strategic/luxury resources and halve their economic progress.
* Blockade enemy civilian ships to destroy them for dust.
* Gain war pressure on your opponent

The first reason for this is that sieging, itself, does no "collateral damage" whilst in progress (i.e. killing populations or system improvements), unlike most types of invasion strategies.

The second reason is that the developers mindfully set up the numbers so that sieging can be used to opt out of a "death spiral" that frequently happens when assaulting a system the enemy truly does not want to lose. On each turn, a defender can issue a "Draft" strategy, and replenish enough manpower to keep on fighting, turn after turn (potentially for a few dozen turns). Any attempts to turn up the heat with more aggressive battle tactics only make the destruction worse, as the system depopulates and loses buildings.

However — if you first siege the system down to zero manpower, **the number of troops raised by "Draft" is something that a reasonably modern/upgraded assault force can often kill outright in a single turn,** especially with a Blitz strategy. If that's all they have, they'll end up near enough to zero to immediately give you a "Decisive Victory", and prevent the trench warfare from ruining the system.

> ℹ️ Note that, unlike many modules, it's legal to equip siege modules on civilian ships, like colony ships. This may or may not be useful depending on the faction you're playing, but it could make them cheaper to field.
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## Invasion Action

Once a system's defenses have been sieged down to your liking, use the Invasion action while your fleet is in orbit to start a ground battle. Your fleet will immediately deploy its entire manpower  stock to the surface and a ground battle will begin. This battle will continue until either side has lost all manpower or surrenders. Similar to sieging, fleets can only begin an invasion if there are no hostile military ships orbiting the same system.

Once an attacker has deployed their manpower, their fleets have no further direct effect; no siege damage is done while an invasion is in progress, and the invasion will continue on its own. They can even return to a friendly system, refill their manpower, then drop off more at the invasion site if it's still going on! However, if all hostile fleets leave the system (so it is no longer under siege), it can refill its Defensive Manpower from the Empire Manpower.

## Invasion Mechanics

Each turn, the attacker and defender both field a certain amount of their banked manpower, according to each one's Manpower Deployment Limit. Having more manpower than your Deployment Limit does not make the battle go any faster, it just ensures you have reinforcements for future turns. Manpower Deployment Limit can be increased by the attacker having sieging fleets with appropriate support modules (such as *OpEx Gear*) or the defender having various System Improvements (such as *Impervious Bunkers*).

The deployed manpower is converted into troops according to each empire's troop distribution rules and the cost of each troop type, and then each does damage to the other in multiple phases, similar to a fleet battle. Each side also chooses a battle tactic, which affects their Manpower Deployment Limit, troop health and damage, collateral damage to population and improvements, and other factors of battle.

If both sides have troops left at the end, the invasion will continue the next turn, until one side completely runs out. If the attacker has ships in orbit, it can choose to retreat after combat, stopping the invasion and moving their troops back up into the ships. Alternatively, the defender can choose to cut their losses and cede the planet, stopping the invasion and letting the attacker win in return for making the attacker's integration of the system take longer (and hopefully allow them to retake the system).

## Manpower vs Troops

The relation between Manpower and deployed troops is not a 1:1 ratio. Every deployed soldier, tank, or aircraft requires multiple points of manpower to deploy, and damage is calculated based on the deployed troops rather than the manpower. The amount of troops deployed per manpower can be improved by some Minor Faction assimilation traits.

The composition of your ground forces is controlled empire-wise from the Military screen by selecting "Manage" under the Troops Breakdown. Adjusting your army composition costs a small amount of Empire Manpower ; each troop type receives bonus damage against one other troop type in a rock-paper-scissors fashion. You can also upgrade your troops to increase their health, damage, and bonus by spending Dust, Resources, and Manpower.

During each round of a ground battle both the attacker and defender can only deploy a limited amount of Manpower. This number can be raised with ship modules, system improvements, or empire improvements (most often, via tech tier unlocks), and is also influenced by the chosen Tactics.

Basic Stats
 Air | 20  | 200 | 95-115

## Tactics

For each turn of the ground battle, both the invader and defender get to choose from three different tactics. These tactics influence the maximum amount of manpower deployed for the battle, the health and damage of participating troops, or flat bonus damage dealt before the battle begins.

* +50% Improvement Destruction
* +50% Population Death
 Guerrilla Warfare
 Blitz
* +25% Improvement Destruction
* +25% Population Death
* -25% Health on troops
 Academy Tactics
(Academy only)
* +20% Population death
 Para-Raiders
(Pirates Only)
* -10% Health on Troops

* *Orbital Bombardment* is useful when the defender's troop composition would otherwise give them an advantage over your army, as you deal some guaranteed damage and can't lose as many troops each turn even in a complete rout. The increased collateral damage makes it generally a less attractive option, however, except against Pirates who have no buildings or pops to destroy in the first place.

* *Guerrila Warfare* is useful when the defender has a manpower advantage, or when it's important to capture the system with as little collateral damage as possible. The extra turns it takes to win a battle, however, increases the chance of your ships being driven away and defensive manpower being refilled.

* *Blitz* is generally the most useful tactic, allowing you to leverage the highest amount of offensive manpower without too much collateral damage, so the battle ends in fewer turns. As the attacker, you'll usually be at the advantage in manpower anyway (especially after a protracted siege), making the decreased health (and thus increased troop deaths) not a significant issue.

* Academy Tactics are only used by the Academy AI-controlled faction, when you've declared war on them, and they're invading one of your systems (typically to reclaim it).

* Para-Raiders actually, remarkably, isn't just used by pirate-fleets invading player-owned systems. It can also be used by player ships masquerading as pirates using the Privateers mechanic.

* *Draft* is one of only three ways for a defender to refill their Defensive Manpower during an invasion, (without driving away the besieging fleet). It also increases your Deployment Limit, letting you deal more damage to the attacker overall. The population cost can be steep, but it's better than losing *all* the population due to an attacker taking the system from you.

> ℹ️Note that, contrary to appearances, that "other way" is not the *Chain Gang* resource improvement — it does not provide additional system manpower during an invasion. Instead, it increases *Empire* manpower, so you get no benefit to that system from using it during an assault.
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> ℹ️That "second way" is to choose "Dark Glitter" as a luxury resource system improvement; amongst other things, it affects the rare Enrollment Rate stat. When you're invaded, each instance of it on a system (potentially up to 3) will create +75 manpower out of thin air (just like Drafting creates +175). Unlike Drafting, there is no cost to it at all. Also, it can be fully stacked with Drafting to make a system hideously difficult to invade (potentially gaining +400 manpower per turn). The only (but significant) downside is the opportunity cost of selecting Dark Glitter rather than another FIDSI-generating luxury development.
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>  The third way is to send a fleet with manpower to the star system that is currently being sieged. If the fleet reaches the destination and stayed there for 1 turn, the manpower on their fleet will be transfered to the ground for battle and reinforcement.
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* *Protect System* is the standard defensive tactic, reducing troop death and collateral damage. Use it whenever you've got a reasonable amount of defensive troops still in reserve.

* *Tactical Surrender* can be used when there's no chance of winning a ground battle, but you have a counter-attacking fleet on the way. It prevents any collateral damage from a protracted fight, and halves the winner's system ownership growth (and defensive manpower regrowth), giving you a larger window in which to easily retake the system.
* Stampede is forced on you against your will. It's a disastrously bad "choice" of strategy which you cannot and would not pick of your own volition. It's caused by your opponent earning a particular hacking outcome — this hacking outcome locks you into using **only** this strategy for the next 5 turns (on normal speed). Since this prevents using the "Draft" strategy, this can cause you to lose a system outright if it's not fortified.
	+ Rarely, though, this tactic can potentially backfire on the hacking attacker. Since this tactic decreases the amount of forces capable of being deployed on the battlefield at a time, it may instead turn into a protracted conflict as even a total win for the attacker would still result in having reserves that will need to be cleared out in the next round of fighting.

* *Sacred Ground* is available only to the Hissho. It is enabled by issuing a  Keii action on either a Behemoth, or a system; once issued, this defensive tactic is available on the affected systems. It is a flatly superior version of "Protect System", and simply does a better job of defense.

* *Academy Tactics* are only used by the "Academy" AI-controlled faction, if you invade one of their systems.

* *Dug-In* is only used by pirate bases, when you try to invade (and thus, destroy) them.

## Outcomes

After winning an invasion the invader may choose to Occupy, Pillage, or Raze the system. Some factions have unique replacement actions that do something extra.