Politics in Julius Caesar is often understood as the interaction of individuals: Brutus, Cassius, Antony, Caesar. In this essay, I argue that the play’s politics instead center on the continuation of the opposition between the two factions of the Roman civil wars: the Marians and the Sullans. By examining Renaissance English accounts of those wars, I demonstrate the importance of that factional division to early modern English thinking about the late Roman Republic and then trace its presence in Julius Caesar. This historically minded approach reveals how much of the play draws on an awareness of these factions, from the invocation of Pompey by the tribunes in the first scene to the division of followers between Antony and Octavius in the last. These factions structure the political world of the play, and the characters’ successes and failures are bound up in their relation to that world. To understand the politics of Julius Caesar, therefore, we must bear in mind the factional lines along which it is built.