"Imperium" is a two-player game simulating a series of conflicts between the emerging Terran (human) Confederation and an immense and ancient alien empire, the Imperium. The Sun and nearby stars lie at the extreme edge of this alien space-faring civilization, and the Terrans struggle to survive and expand against this powerful state. While the Terran player is in control of the entire Confederation military, the Imperial player represents a low-ranking provincial governor on the frontier, who is forced to petition the central government for reinforcements and is occasionally subject to its meddling.