Land warfare

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This article is for the PC version of Stellaris only.

War

Warfare

Space warfare

Land warfare

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.

Combat

Although secondary to space battles, ground warfare is a vital aspect of many wars.

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:

Morale Perc.	Penalty
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.

Army rank

Rank	Exp Points	Effects
Regular	0 - 100	None
Experienced	100 - 1000	+10% Damage +10% Morale
Veteran	1000 - 10000	+20% Damage +20% Morale +10% Health
Elite	≥ 10000	+40% Damage +40% Morale +20% Health

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 modifiers

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.

Source	Army Health
Lithoid species trait	+50%
Clone Soldier Ascendant species trait	+25%
Global Defense Grid technology (Defense armies only)	+25%
Resistance is Frugal tradition (Defense armies only)	+25%
Nerve Dampeners technology	+10%

Defense armies

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

Assault armies

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.

Type	Cost	Time	Upkeep	Base Damage	Morale Damage	Collateral Damage	Health	Morale	War exhaustion	Requirements	Species
Assault Army	100	90	1	1.50 - 3.00	1.50 - 3.00	100%	200	200	100%		Biological
Slave Army	50	60	0.5	1.50 - 3.00	1.12 - 2.25	150%	200	150	50%	Slave Processing Facility	Biological (enslaved)
Clone Army	75	30	0.75	1.50 - 3.00	1.50 - 3.00	125%	200	200	50%	Gene Banks	Biological
Robotic Assault Army	150	90	1.5	1.50 - 3.00	1.50 - 3.00	150%	400	Immune	50%	Droids Robotic Workers Allowed	Robot
Psionic Army	250	120	2.5	3.00 - 6.00	4.50 - 9.00	50%	350	500	300%	Telepathy	Biological (psionic with Utopia)
Xenomorph Army	200	100	2	3.00 - 6.00	6.00 - 12.00	500%	400	Immune	25%	Morphogenetic Field Mastery	None
Gene Warrior Army	300	150	3	3.00 - 6.00	3.00 - 6.00	75%	500	500	300%	Gene Seed Purification	Biological
Undead Army	100	60	0.75	1.50 - 3.00	2.40 - 4.80	125%	200	Immune	50%	Necromancer jobs	Biological
Hunter-Killer Army	100	90	1	1.50 - 3.00	1.50 - 3.00	200%	200	Immune	50%	Machine Intelligence	Robot
Battle Frame Army	200	120	2	2.25 - 4.50	3.00 - 6.00	200%	500	Immune	100%	Machine Intelligence Adaptive Combat Algorithms	Robot
Mega-Warform	800	500	8	6.00 - 12.00	9.00 - 18.00	400%	1200	Immune	400%	Machine Intelligence Biomechanics	None
Cybrex Warform	250	500	8	7.50 - 15.00	15.00 - 30.00	500%	1400	Immune	400%	Cybrex War Forge relic Can only be recruited on the capital	None
Titanic Beast	300	90	1	4.50 - 9.00	9.00 - 18.00	300%	1000	600	200%	Titanic Lifeforms event chain Only 3 can be recruited	None
Azizian Army	250 50	90	1	4.50 - 9.00	9.00 - 18.00	100%	1000	400	100%	Ice Alien event chain Only 3 can be recruited	None
Imperial Legion	300	150	3	3.75 - 7.50	3.75 - 7.50	75%	600	600	300%	Galactic Emperor Imperial Legions resolution Only 12 can be recruited	None
Mercenary Army	120	0	2	1.65 - 3.30	1.65 - 3.30	250%	200	100	50%	Mercenary enclave deal	Biological
Mechanized Mercenary Army	240	0	5	3.3 - 6.6	3.3 - 6.6	300%	360	200	50%	Mercenary enclave deal	Biological
Psionic Avatar	Event	0	0	7.50 - 15.00	15.00 - 30.00	100%	1400	Immune	500%	Shroud event	None
Nanite Warform	Event	0	0	15.00 - 30.00	90.00 - 180.00	500%	3600	Immune	400%	A Quiet Stroll event	None
Skeletal Giant	Event	0	1.5	4.50 - 9.00	13.50 - 18.00	350%	1400	Immune	50%	Reanimators Strange Mountain Formation anomaly	None

Orbital bombardment

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.

Stance	Planet damage	Army damage	Pop kill chance	Other effects	Requirements
Selective	50%	100%	25%	Does not kill the last 21 Pops Does not bomb planets with no armies on it	None
Indiscriminate	100%	150%	50%	Does not kill the last 11 Pops	Not Pacifist
Armageddon	150%	200%	100%	If the last pop is killed, the planet becomes a Tomb World	Any of: Fanatic Purifiers Determined Exterminator Become the Crisis
Javorian Pox	20%	150%	150%	Does not kill Mechanical Pops If the last pop is killed, the planet becomes a Tomb World	Javorian Pox Sample relic activation Not Pacifist
Raiding	100%	50%	100%	Abducts pops instead of killing them Species with Displacement, Neutering or Extermination species rights will still be killed Does not cause Terror Bombing opinion if successfully abducted Does not kill or abduct the last Pop	Either: Barbaric Despoilers Nihilistic Acquisition

Orbital Bombardment Damage dealt to enemy planets can be increased by the following:

Source	Damage
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:

Source	Damage
Subterranean origin	−75%
Planetary Shield Generator building	−50%
Survival of the Fittest tradition	−25%
Never Surrender tradition	−25%
Fortress World designation	−10%
Fortress Station designation	−10%

Devastation

Devastation	Orbital Bombardment		FTL inhibitors	Tree of Life	Time To Recover
Devastation	Damage to armies	Kills pops	FTL inhibitors	Tree of Life	Time To Recover
0%-24.9%	50%		Functional	Alive	498
25%-49.9%	100%		Functional	Alive	998
50%-74.9%	100%		Disabled	Destroyed	1498
75%-100%	200%		Disabled	Destroyed	2000

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.