Sid Meier's Alien Crossfire (also called SMACX or just SMAX) is an expansion pack to Sid Meier's Alpha Centauri, which was released by Firaxis Games. Both pre-patched games were later bundled together in the Alpha Centauri Planetary Pack.
There are seven new factions added to the game, five of them human and two of them alien. The two alien factions are determined to destroy each other, humans just caught in this alien crossfire, thus the name of the expansion pack.
For diplomatic victory, you must eliminate any alien faction first.
An alien faction can win by completing the Resonance Communicator, and signalling their people to send a fleet to wipe out everyone else.