Wars are not decided only in space. In order to capture enemy planets, entire armies are needed, along with the preparation and battlefield awareness to properly use them. However, planets may only be invaded if the system's starbase has been occupied.
Ground combat takes place between the planet owner's armies and the invader's armies. The number of armies that can be engaged in combat on either side is five plus one-fifth of the planet size. Excess armies are initially placed in a reserve area behind the frontline and replace any disengaged or destroyed armies as combat progresses.
Each day, each army engaged in combat deals its health and morale damage to a randomly selected enemy army; armies with less than 50% health are twice as likely to be selected. Armies below 50% health may also disengage from battle; this moves them from the frontline area to the reserve area. Disengaged armies cannot return to the frontline but can still be attacked by enemy armies and destroyed. Disengaged armies are half as likely to be selected as the target of an enemy army. Whenever an army is destroyed, there is a 5% chance for the general leading that army to be killed as well.
Unless an army is immune to morale damage, when its morale drops below certain thresholds, the army will be negatively affected with the following modifiers:
|50% <||−25% Army damage|
|0%||−75% Army damage|
After 30 days, the attacker can choose to retreat at any time. However, there is a chance that each retreating army is destroyed while attempting to return to space, with the chance increasing as the army is more damaged. This makes retreating a risky endeavor and something to do only in very poorly chosen engagements.
As long as the ground combat is ongoing, it is possible for either side to land reinforcements, though typically this will only be feasible for the attacker. The ground combat ends when the attacker retreats or all armies of either side are destroyed.
|Regular||0 - 100||None|
|Experienced||100 - 1000|| +10% Damage|
|Veteran||1000 - 10000|| +20% Damage|
|Elite||≥ 10000|| +40% Damage|
As armies fight battles, they will increase in rank, improving their stats based on their experience points. Armies get +2 experience points each time they deal damage and +1 when they take damage. Army starting experience can be increased by +100 by each of the following:
- Strength of Legions civic
- Private Military Companies civic
- Military Academy building
- Dread Encampment building
- Mercenary Liaison Office Corporate holding
- Pirate Free Haven Corporate holding
Army stat modifiersEdit
In addition to army rank, several technologies, civics, species and leader traits, and other sources affect army damage, health, and other stats. Additionally, generals provide +5% army damage per level and plus other bonuses from traits. Modifiers from species traits affect armies recruited from that species, while general and governor traits affect armies led by that general or on planets in that governor's sector. The following is a partial list of army stat modifiers.
|Lithoid species trait||+50%|
|Clone Soldier Ascendant species trait||+25%|
| Global Defense Grid technology
(Defense armies only)
| Resistance is Frugal tradition
(Defense armies only)
|Nerve Dampeners technology||+10%|
Defense armies are automatically recruited by certain jobs, based on the species working that job, and can be organic or robotic. Defense armies cannot be moved from the colony they are recruited on and are used only to defend against enemy armies. While they are stronger one-for-one than assault armies and their loss does not cause war exhaustion, their limited recruitment means that significant investment is necessary to fend off a concentrated attack.
The type of army recruited depends on the pop working the building that spawns them. Defense armies do not incur any upkeep beyond that of the building and pop which creates the army. Defense armies do not cause collateral damage.
|Type||Base Damage||Morale Damage||Health||Morale||Source|
|Defense Army||2.25 - 4.50||2.25 - 4.50||250||250||Organic +1 +2 +2 +3|
|Robotic Defense Army||1.50 - 3.00||1.50 - 3.00||250||Immune||Robot +1 +2 +2 +3|
|Undead Defense Army||2.25 - 4.50||3.93 - 7.87||350||Immune||Organic +1 +2 +2 +3 +3|
Replaces normal organic defense armies if at least one necromancer is present
|Offspring-Led Army||2.62 - 5.25||3.41 - 6.82||400||Immune|| Progenitor Hive +2 +3|
Replaces normal organic defense armies if at least one Offspring Drone is present
|Drone Grid||1.65 - 3.30||1.65 - 3.30||220||Immune||Machine Unit +2 +3|
|Event spawned defense armies|
|Sentinels||6.00 - 12.00||30.00 - 60.00||1400||Immune||Archaeology site event outcome|
|Crystalline Bane||52.50 - 105.00||2625.00 - 5250.00||11000||Immune||Unexpected Mineral Seams|
An empire can recruit assault armies from a colony based on the species living there. The species must not have Exempt Military Service rights in order to recruit an army from that species. An empire cannot recruit more assault armies from a species than the total number of pops of that species living in the empire, with the exception of Clone Armies. Armies not tied to a species, such as the Xenomorph Army, are unlimited unless otherwise specified.
Unlike defense armies, assault armies are based primarily in space and each recruited army boards a transport ship. Transport ships are unarmed but automatically upgraded with the latest defense and utility components. Assault armies can also be ordered to land on any controlled planet to provide additional defense against invasion.
Orbital bombardment occurs when a fleet is in orbit around a hostile colony and is generally a precursor to invasion. Genocidal empires can even opt to skip the invasion entirely and simply exterminate all life on the colony. Orbital bombardment causes damage to any armies as well as devastation. Effectiveness is based on the Fleet Size of the fleet in orbit, where maximum effectiveness is reached at 200 or larger Fleet Size. Assault armies take 5 times more damage from orbital bombardment than defense armies.
Orbital Bombardment Damage dealt to enemy planets can be increased by the following:
|Overwhelming Force tradition||+20%|
|Orbital Trash Disperser component||+25%|
|Munitions Plant juggernaut aura||+30%|
|Crisis level 3||+20%|
Orbital Bombardment Damage taken from enemy fleets can be reduced by the following:
|Planetary Shield Generator building||−50%|
|Survival of the Fittest tradition||−25%|
|Never Surrender tradition||−25%|
|Fortress World designation||−10%|
|Fortress Station designation||−10%|
|Devastation||Orbital Bombardment||FTL inhibitors||Tree of Life||Time To
|Damage to armies||Kills pops|
Devastation is a measure of how much damage has been caused to the colony's infrastructure. It goes from 0 to 100%, and every 1% devastation causes a 1% decrease in housing, amenities, trade value, resources from jobs, upkeep from Jobs, growth speed and immigration pull.
Devastation is primarily caused by orbital bombardment, and to a lesser degree assault armies. Assault armies have a Collateral Damage modifier that determines how fast they cause devastation. Defense armies do not cause any devastation.
Devastation decreases by 0.05% daily if the colony is not being invaded or bombarded.