Sid Meier's Alien Crossfire, commonly abbreviated SMAXSid Meier's Alien Crossfire (Cross = X), is the title of the official expansion pack to Alpha Centauri developed by Firaxis Games, released in 1999. In contrast, SMACSid Meier's Alpha Centauri is used to refer to the vanilla or unexpanded game.
The expansion pack introduced many content additions and rule changes that set it apart from SMAC. Some of these are listed below.
- Several new factions, including two Alien factions with their own unique victory condition that are permanently embroiled in civil war with each other.
- Tech tree expansions.
- PBEM support.
- Committing 12+ atrocities (dependent upon difficulty level) will lead to all factions declaring Vendetta.
- Nerve stapling becomes increasingly ineffective the more it is used at a particular base.