In Warhammer 40,000, the galaxy’s great factions usually have a very serious reason for going to war. The Imperium fights to survive, the Aeldari try to stave off extinction, the Necrons want to restore their empire, and the forces of Chaos pursue ambitions of their own. Even the Tyranids, alien as they are to most other civilizations’ concerns, obey an implacable logic: find biomass and devour it.