The Alliance is known as a participant of the historic War of Sol which culminated with the Alliance launching their escape from the Solar System.
The Great War
During the War of Sol, two blocs fought for complete control over the Sol System: the Alliance and the Coalition. The Alliance was composed of the democratic nations of the United States, Western Europe, Japan, and Australia. For decades, constant fighting between the two factions ensued, with neither side gaining the upper hand for long.
In 2160, the Alliance proposed and signed a peace treaty between the two blocs, but as the Coalition admiral headed to Europa (one of Jupiter's moons) to sign it, he ordered a Coalition fleet to de-cloak and attack the Alliance fleet, who had stood down from battle after hearing about the treaty. Instead of ending the war peacefully, they destroyed the French and Italian fleets and took control of all the inner planets, including Earth, and most of the outer planets, excluding Neptune. Two years later, the Alliance recovered the outer planets and began its assault on the inner planets. Eventually, the Coalition was beaten back to Mercury. However, by some unknown means, the Coalition gained the upper hand and began to counterattack, eventually retaking every planet in Sol.
Shortly after the Exodus of the Five Sleeper Ships, the Coalition arrived on Dwarf Planet Pluto, the last stronghold of the Alliance. As the last defenders of the planet prepared for battle, a Nomad superweapon arrived and destroyed the Sol System, wiping out all traces of humanity.
Today, the Alliance's culture and way of life is continued by the existance of the Seven Houses of Sirius (the Liberty Republic, the Kingdom of Bretonia, the Kusari Empire, the Federal Republic of Rheinland, the Corsair Empire, the Nation of Maltese Outcasts, and the Kingdom of Gallia. The Hispania sleeper ship was disabled by Coalition saboteurs and the colonists within divided into the unlawful Corsairs and the Outcasts).
However, the Alliance powers have become divided in the 800 years of living in Sirius. The first conflict to start was the Hispanic Civil War, also known as the Corsair-Outcast War. Second was the War of Tau, a war started between Bretonia and Kusari over a territorial dispute in the Tau Border Worlds. Third was the Liberty-Rheinland War, which started due to news reports that Liberty was performing experiments on live Nomads, which Liberty condemned. Another cause of that war was a Rheinland invasion in the Liberty Border Systems, which Liberty responded to with a trade embargo. The most recent war to start was the Gallia-Sirius War. Technically, this war hasn't started yet due to the Council, a group of Gallic citizens who believe Gallia's planned war with the rest of the Alliance powers was a huge mistake, revealing the existance of Gallia much earlier than the Gallic leaders intended. Prior to the Exodus of the Five Sleeper Ships, three addtional sleeper ships had been launched, but they were destroyed by the Coalition. One of those 3 ships was the French Gallia. When the Alliance said they could not fund the construction of a second sleeper ship for the French, the French viewed this as betrayal and secretly built a second ship to escape to Sirius. Since arriving, the French Gallics have been plotting for revenge against the Alliance.