The Great Spiral
Terrans are humans, originating from the Sol system in the Milky Way galaxy. After discovering FTL technology, the species was ravaged with war, until one side was forced to surrender and was exiled from their home galaxy. After nineteen thousand years of travelling in cryosleep, they finally made it to the Pinwheel Galaxy, where they quickly colonized many star systems and ultimately(through yet more war) became the undisputed rulers of the galaxy. This marked year Zero, Post-Exodus.