Alien Crossfire introduces five new human and two non-human factions, as well as additional technologies, facilities, secret projects, native life, unit abilities, and a victory condition.

Critics praised its science fiction storyline (comparing the plot to works by Stanley Kubrick, Frank Herbert, Arthur C. Clarke, and Isaac Asimov), the in-game writing, the voice acting, the user-created custom units, and the depth of the technology tree.

[8] Immediately prior to the start of the game, a reactor malfunction on the Unity spacecraft wakes the crew and colonists early and irreparably severs communications with Earth.

[9] After the captain is assassinated, the most powerful leaders on board build ideological factions with dedicated followers, conflicting agendas for the future of mankind, and "desperately serious" commitments.

[13][16] Each faction excels at one or two important aspects of the game and follows a distinct philosophical belief, such as technological utopianism, Conclave Christianity, "free-market" capitalism, militarist survivalism, Chinese Legalism, U.N. Charter humanitarianism, or Environmentalist Gaia philosophy.

[30] Thus, Alpha Centauri closes "with a swell of hope and wonder in place of the expected triumphalism", reassuring "that the events of the game weren't the entirety of mankind's future, but just another step.

In addition to terraforming, optimizing individual base performance and building secret projects, players may also benefit their factions through social engineering, probe teams, and diplomacy.

[11][14][17][18][38] Probe teams can sabotage and steal information, units, technology, and energy from enemy bases, while diplomacy lets the player create coalitions with other factions.

[41] The game's basic rules, diplomatic dialog, and the factions' starting abilities are in text files, which "the designers have done their best to make it reasonably easy to modify..., even for non-programmers.

"[42][43] Alpha Centauri supports play by email ("PBEM") and TCP/IP mode featuring simultaneous movement, and introduces direct player-to-player negotiation, allowing the unconstrained trade of technology, energy, maps, and other elements.

Disagreements between the new management and its employees prompted Reynolds, Jeff Briggs, and Sid Meier (designer of the original Civilization) to leave MicroProse and found Firaxis.

[47] His inspiration included "classic works of science fiction", including Frank Herbert's The Jesus Incident and Hellstrom's Hive, A Fire Upon the Deep by Vernor Vinge, and The Mote in God's Eye by Larry Niven and Jerry Pournelle for alien races; Kim Stanley Robinson's Red Mars, Slant by Greg Bear, and Stephen R. Donaldson's The Real Story for future technology and science; and Dune by Herbert and Bear's Anvil of Stars for negative interactions between humans.

Alpha Centauri B is also dubbed Hercules, a reference to him killing several centaurs in mythology, and the second star preventing the formation of larger planets.

[47][51] Reynolds cited the Alpha Centauri's balance for the greater sense of urgency and the more pressing pacing than in his earlier game, Sid Meier's Colonization.

[47] According to producer Timothy Train, in designing the strengths and weaknesses of the factions, the goal was to suggest, without requiring, certain strategies and give the player interesting and fun things to do without unbalancing the game.

[63] The goal was a product of unprecedented depth, scope, longevity, and addictiveness, where the player is always challenged by the game to come up with new strategies with no all-powerful factions or unstoppable tactics.

[71] A month after Alpha Centauri's February 1999 release, the Firaxis team began work on the expansion pack, Sid Meier's Alien Crossfire.

[57] The development team included Train as producer and designer, Chris Pine as programmer, Jerome Atherholt and Greg Foertsch as artists, and Doug Kaufman as co-designer and game balancer.

[76] The developers eventually provided the aliens with Battle Ogres, a Planetary survey, non-blind research, and other powers to produce "a nasty and potent race that would take the combined might of humanity to bring them down".

[6][80][81][82] Alpha Centauri received wide critical acclaim upon its release,[83][84] with reviewers voicing respect for the game's pedigree, especially that of Reynolds and Meier.

[85][86] The game was favorably compared to Reynold's previous title, Civilization II,[6][87][88][89] and Rawn Shah of IT World Canada praised the expansion for a "believable" plot.

[102] Aaron John Loeb, the Awards Committee Chairman, said "for those that understand the intricacies, the wonder, the glory of turn based 'culture building,' this is the game worth skipping class for.

"[103] Alpha Centauri's science fiction storyline received high praise; IGN considered the game an exception to PC sci-fi cliches,[87] and GamePro compared the plot to the works of writers Stanley Kubrick and Isaac Asimov.

[93][94] The artificial intelligence of computer-controlled factions, which featured adaptability and behavioral subtlety,[106] was given mixed comments; some reviewers thought it was efficient and logical,[87][88] while others found it confusing or erratic.

[93][94] Edge was disappointed in the game's diplomacy, finding "no more and no less than is expected from the genre" and unhappy with "the inability to sound out any real sense of relationship or rational discourse.

[110] The editors of PC Gamer US named Alpha Centauri their "Best Turn-Based Strategy Game" of 1999, and wrote that it "set a new standard for this venerable genre.

[112] Alien Crossfire was a runner-up for Computer Games Strategy Plus's 1999 "Add-on of the Year" award, which ultimately went to Heroes of Might and Magic III: Armageddon's Blade.

[113] There have been no direct sequels beyond Alien Crossfire, something that writer Greg Tito attributed to Reynolds leaving Firaxis in 2000 to form Big Huge Games.

[114] However, a spiritual sequel, Civilization: Beyond Earth, was announced by Firaxis in April 2014 and released on October 24, 2014; several of those that worked on Alpha Centauri helped to develop the new title.

Writer Steve Darnall and illustrator Rafael Kayanan also made a graphic novel entitled Alpha Centauri: Power of the Mindworms.