A group might, despite the availability of space, just like taking other folks stuff, rather than making the stuff for themselves. Or, other similar creatures might be raw resources, as in Jupiter Ascending. Or, a civilization or race may be inherently warlike, for example, 40K orcs, or Saberhagen’s Berserkers. Or, war might be used to stabilize a political order. Or as a way to realize warrior or spiritual ideals. Or might be instigated for entertainment, or cruelty, or to destabilize one or more civilizations, perhaps to prevent further advancement. Or one civilization might find another‘s practices morally appalling.
Be safe and well,
‘Tom Bitonti