The Stellar Alliance (星系連合, Seikei Rengō) was a group of planets that ruled over the colonial worlds before the War of Independence. At the end of the war, the alliance was absorbed by Galactic Empire along with the Colony Federation .
The Stellar Alliance consisted of suzerain planets that ruled over newly colonised worlds. However, as time passed and populations grew, relationships between the suzerain and colonial worlds worsened, eventually leading to the War of Independence .
The Stellar Alliance boasted about having a few Strategic battleships that were very powerful in ship to ship combat during the War of Independence 
In the last days of the war, the Stellar Alliance poured its resources into developing a superweapon, the Stellar Slayer, to demonstrate its might to both the Colony Federation and the Galactic Empire. However, progress was not fast enough and with the empire's forces closing in, the alliance intended to use the weapon in a different way - as a supernova bomb that will devastate an area light-years across. The Colony Federation unfortunately found out about the intentions of the alliance and with the aid of their pirates, thwarted the plan in a battle over Garnet A. Not long afterwards, both the Colony Federation and the Stellar Alliance surrended to the Galactic Empire's overwhelming forces which eventually resulted in their absorption into the empire .