The Galactic Alliance of Humankind also known Galactic Alliance or Galactic Alliance of Humanity or Galactic alliance of Mankind is the government that rules the human space colonies.
The GAH is believed to be the direct descendant of the Continental Union. The CU was directly opposed to a group known as the Evolvers, the predecessors of the Hideauze. When Ledo finds the ancient lab and reads the records, it is revealed that Evolvers were looking to escape from Earth's upcoming ice age. At the time, there was no way for anyone to survive a long trip in space, so the Evolvers solution was to genetically alter themselves to be able to live in space without the need for oxygen. This was opposed by the CU, which resulted in large scale battles between the two sides. Eventually, the CU created a wormhole gate in order to escape Earth and had planned to leave the Evolvers stranded on Earth, but the Evolvers took the gate. Both factions escaped Earth and the CU eventually became the GAH. The great space colony of Avalon was eventually constructed and would become the Alliance's "homeland", home to 470 million people.
The Alliance is currently still fighting the Hideauze, Ledo is too far away from them (approximately 6500 light years to the closest known Galactic Alliance base according to Chamber) to find out. A recently revealed spy among the Gargantia Fleet reveals the Alliance is aware of Earth and its condition. It is likely the Alliance is keeping the Hideauze contained at the Hot Jupiter planet. If the Hideauze learn that the Earth is once again habitable, the war would be drawn back to Earth.
It is unknown or not the Alliance is gonna retake the planet or not. Despite their technological advancement, they never seem to try to terraform or colonize any others planets.
In the Alliance, people who are ill and unable to fight are often sent into space where they inevitably die. Citizenship is given to soldiers after 145,000 hours of service, after which they are allowed to visit Avalon for a few weeks.
Anyone who rejects the Alliance are considered to be Drifters.
According to Kugel, the knowledge of of the truth behind the fact that Hideauze used to be human only known to the higher-ups in the GAH.