Imperium is a 2-player game of space empire conflict set in 22nd Century AD, and shortly after release, retconned into the history of the Traveller role playing game. It simulates the clash between Earth (Terra) and an alien civilization, represented in the form of a widespread Empire (the Ziru Sirka). Both sides have a variety of star-ships and ground forces to choose from, and the game is notable for how the two sides are asymmetrical: their forces aren't identical and their economies work differently.
Movement takes place via 'jumps' from one star to the next, and conflict is resolved at these 'points'. There are two types of star-ship weaponry, short-range beam factors, and chiefly long-range missile factors also used for planetary bombardment.