The Andromeda Alliance was a resistance and military alliance in the League and War Eras.

Colonies in Andromeda and the Wike Grikele region of Sagittarius remained outside of Galactic Defense League control, and began to form defensive pacts to prevent that control from expanding over them. As popular resentment against the League grew, the Andromeda Alliance became more organised, and even began to support resistance movements inside League territory. For the most part, this activity was successfully kept secret, as GDL ships rarely ventured outside their space.

The clandestine campaign against the League came to a head at the end of the 44th century, with unrest boiling over in response to a number of heavy-handed GDL actions. In 4404, Director Kowalski of the Alliance gave the order to begin full-scale military operations against the League in a massive surprise attack.

The War began with Alliance fleets conducting deep strikes against GDL centres of command and administration. Despite the unexpected nature of the attack, the sheer size of the GDL Navy meant several battlegroups were unscathed in the initial strikes and were able to respond quickly, resulting in a number of pitched battles with Alliance forces as they attempted to maraud through League space. Notable engagements of this early stage of the war included the Battles of Genevieve and Tau Ceti, where the Alliance's advanced warships were able to exploit the stagnant doctrine and technology of the GDL Navy to inflict severe losses.

Despite early successes, including a dramatic strike on Earth itself in mid-4404, the war eventually turned against the Alliance as the League shifted its behemoth industrial power to a war footing. The Alliance was also hampered by a desire to avoid collateral damage which the League did not share. GDL warships would often bombard ground positions indiscriminately rather than deploy troops to face Alliance units on unfavourable terms.

By the end of 4405, GDL forces were conducting counter-attacks into Alliance territory in Andromeda. A devastating engagement at Medusa 5-9 in December cut off the remaining Alliance forces in Sagittarius from their strategic supply lines, and forced the majority of the Alliance fleet to withdraw into the Landfall region.

The Alliance had one more trick up their sleeve. A bold deception operation drew the bulk of the GDL fleet into the stellar nebula at Sargasso. There, the best elements of the Alliance fleet pinned the enemy until the RAINDANCE superweapon could be deployed. Built with reverse-engineered Staiide hyperlight technology and rushed to completion in the last weeks of the war, this weapon caught the GDL Navy completely by surprise. The League's most powerful force was shattered.

Director Kowalski met General Xiang Storm for peace talks after the battle, proposing a truce on the grounds that neither side had the resources remaining to launch a successful assault. At the talks, Kowalski pulled off one more surprise twist in a daring raid that ended with Storm's death.

With Storm dead and the fleet in disarray, the League's command structure crumbled. The Alliance was able to move in and finally bring an end to the Galactic Defense League's thousand-year reign.

Now in effective control of all inhabited space in Sagittarius and Andromeda, the Alliance had to transition from a military alliance to a civilian government. In the process, the Andromeda Alliance was reformed into the Core Governance.