The Culture is basically a version of The Federation that very actively meddles with more primitive civilizations for what it believes are altruistic reasons, and often using an ends justify the means logic. In alternating chapters, Use of Weapons focuses on the life history and latest exploits of a strategic genius that the Culture moves from planet to planet to help their favored side in a war. I don't want to say more, but the resolution of the story is great, and a popular discussion topic on sites like Reddit.