Supreme Commander: Forged Alliance

The setting of Supreme Commander is a future in which humanity is able to travel through the galaxy quickly using a quantum tunnel, a portal opened in the fabric of space leading to a designated location potentially light-years away.[5] Tunneling let humankind establish many colonies, which were governed by a centralized Earth Empire. As the number of human worlds grew, however, its control eventually weakened, and the Empire collapsed. The Empire's remnants formed the United Earth Federation; a race of cybernetically-enhanced humans seeking independence formed the Cybran Nation; and colonists who befriended and embraced the religion of the dying alien seraphim formed the Aeon Illuminate. The three factions came into conflict, starting the Infinite War. One thousand years later, the events of Supreme Commander take place, ending the war.

All three endings (one for each faction) for the Supreme Commander campaigns feature teaser endings after the credits as a reference to the (then unannounced) upcoming expansion. The Cybran ending shows the Quantum Artificial Intelligence (QAI) supercomputer calling in unidentified enemies, and then to Dr. Brackman's horror, saying "They are coming". The Aeon ending simply depicts Princess Rhianne, the leader of the faction, opening her eyes in shock and exclaiming "No!". The UEF ending shows many unidentified radar signatures appearing near the location of Black Sun on Earth.

The new playable faction, the Seraphim, are a race of aliens long thought to have gone extinct. The colonists who befriended and embraced the religion of the dying alien seraphim formed the Aeon Illuminate.

The game takes place shortly after the first game, which ended with the firing of the Black Sun, a powerful weapon capable of firing a beam through the Quantum Gates to destroy enemy planets. The Seraphim, a race long thought to have gone extinct, have exploited the firing of Black Sun to create a rift from the Quantum Realm they inhabit to our universe, on Earth. Once through the rift, they wreak a path of destruction through the civilized galaxy, leaving Earth and most of the core worlds of the UEF in ruins. With most of the UEF's key political and military leaders lost, including General Samantha Clarke who died while fighting on Capella, General Hall and Brigadier General Fletcher lead the last of the UEF Military. QAI, the once-loyal Cybran supercomputer built by Dr. Brackman, has been compromised and is waging war on behalf of the Seraphim. It cripples the Cybran Nation's military, forcing Dr. Brackman and Dostya to retreat to the further reaches of space. The Aeon Illuminate are divided over the arrival of the murderous Seraphim from whom they once learned what seemed the peaceful Way; many take sides with the Seraphim as the Order of the Illuminate, led by Evaluator Kael, and brand Princess Rhianne a traitor and heretic. Crusader Rhiza leads a handful of forces loyal to the Princess in a guerrilla-style campaign. Shortly afterward, the UEF and Cybran factions ally and form the Coalition against the Seraphim, with the Aeon Loyalists joining afterward despite Dr. Brackman's reservations.

Before battle commences in the first mission, the player must choose a faction to swear loyalty to. This can be the UEF, Cybran Nation, or Aeon Illuminate loyal to Princess Rhianne. The overall plot and outcome of the campaign remains the same, although certain commanders respond differently or reveal different information to the player at several points in the campaign.

The game begins with the protagonist defending the Coalition base on Griffin IV, the last major UEF base and last line of defense against the seemingly inexorable onslaught of the Seraphim. Order forces are attacking the base and the player is being gated in to hold the line. After the player chooses a side and helps Fletcher hold back the attacking Seraphim and Illuminate, it is discovered that Princess Rhianne of the Aeon Illuminate, thought to have been killed by the Order, is alive, hiding in her palace. She is rescued by Coalition forces, and is able to organize many disenfranchised Aeon who are troubled by the actions of the Seraphim and the Order. It is also discovered that there is a traitor within the Coalition, who is leaking information to the Seraphim and the Order of the Illuminate. Both the UEF and Aeon focus on reorganizing their forces while the Cybrans focus on uncovering the identity of the traitor. Cybran forces loyal to QAI are also encountered during several key battles.

During the fourth mission, the traitor is eventually revealed to be Hex5, formerly loyal to Dr. Brackman and Dostya, now serving QAI referred to as "The Master". Hex5 ambushes and kills Dostya, forcing the player to survive a difficult defense until they are recalled. Immediately afterward, the Coalition discovers that the rift from the Quantum Realm is unstable, and that the massive onslaught that has devastated their worlds and from which they are only beginning to push back is merely the first wave. The Seraphim are building a Quantum Arch on Earth to stabilize the rift; once its construction is completed, no one will be able to survive the armada of Seraphim that will flow through it. Thus, the Coalition plans to launch an all-out assault on Earth.

Dr. Brackman personally vows to destroy QAI, and therefore accompanies the player after Hex5 is destroyed in an experimental Megalith assault bot to destroy QAI. Afterwards, they use a Seraphim portal to gate directly to Earth, where the final assault is being prepared. Aeon loyalists led by Rhiza and UEF forces led by Fletcher are quickly organising. However, as the player progresses to destroying the Arch, Fletcher suddenly succumbs to the UEF's former xenophobia, quickly regarding all Cybran and Aeon as enemies. Despite General Hall's attempt to defuse the situation, Fletcher rebels against Rhiza and the player, even if the player's chosen faction is UEF, while announcing his plans to reactivate Black Sun. He is eventually stopped before the player proceeds to the Arch and successfully destroys it. Immediately afterward, Princess Rhianne enters the rift to the Quantum Realm and seals it from within, destroying the Seraphim's only way of accessing our universe and saving humanity. By doing so, she sacrifices her life, but brings an end to the Seraphim War.

At the end of the campaign, QAI reboots itself and seem to be coming back online. However, QAI's condition and loyalty is unknown. It is possible that the cutscene was meant as a teaser for another sequel titled Experimentals (which has been cancelled).

After the official support by GPG ended with the beta patch 3603 in 2009[14] and the shutdown of the multiplayer backend GPGnet in 2012[15] the game community took over the support of the game, with a Server emulator. A multiplayer client was created by the Forged Alliance Forever community[16][17] and has been running since 2011[18] and since its release many of the players have migrated across. The client features many upgrades to the official one, including a working replay vault, live replays, allowing watching of ongoing games, a mod vault and a map vault. Also, the FAF community has continued to balance and patch the game with own-made so called community patches. Several new modes are also available, including a four-way war between factions over a galaxy spread of planets, a co-operative campaign for the original Supreme Commander campaigns and the Forged Alliance campaign. As of July 2021, FAF continues to be developed, and has seen a steadily increasing playerbase and continued participation in community hosted tournaments,[19] with some of the matches replayed and commentated since 2013.[20]