When the last combat/transport unit defending a base (or non-combat if no combat units present) is destroyed, the population is reduced by one (unless the base has a Perimeter Defense) and it may be captured by opposing factions or attacked by native life forms.
Land bases may be captured by land combat units, while sea bases may be captured by sea combat units or land combat units with Amphibious Pods. Air combat units which do not refuel (Gravships and Locusts of Chiron) may capture any undefended base, but those which do refuel (Needlejets and Copters) may not capture bases.
A captured base passes into the control of the attacking faction. Conquering a base destroys a random number of the base’s facilities (but not Secret Projects) and reduces the population of a base by one. The capturing unit is fully repaired (unless it is a Battle Ogre).
When a human conquers a Progenitor base, or vice versa, the population of the base is reduced to one with half the population killed and the other half fleeing into adjacent squares in escape colony pods.
If a wild native life form enters an undefended base, it destroys one random facility or devours one population then disappears.
If the base population is reduced to zero in combat or through capture, the base ceases to exist. Any Secret Projects within it are lost forever, to all factions.