From the Introduction:
You are a Space Marine, named because of an ancient trademark dispute that only ended when the XIVth Void Commando Group said "fuck the law" not with words but with relativistic kinetic weapons. Also, because "Space Naval Infantry" is nowhere near as catchy. The Space Marines are the vanguard of an aggressively hegemonizing starfaring civilization.
Upon encountering a new world, you strap into a four ton combination of vacuum suit, combat armour, and recreational tank. You use a range of improbably large weapons designed to make other living beings die messily - and to make a range of toasted bread products to keep your morale high. You attempt genocide of the natives until they capitulate to your civilization's rules
This is not a game about ultraviolent imperialsm. This is a game about being an ultraviolent imperialist.