The Wikipedia:Andromeda Galaxy was the second place outside the Milky Way to be colonised by humanity. The first attempt failed, falling into orbit around Torei's star and beginning its terraforming process there. Andromeda is now the hub of intergalactic human civilisation, with the Milky Way cultures having become stagnant.
Long long ago, back when humanity had only begun to spread out of its spiral arm of its home galaxy, an empire had ambitions. This empire, known only to history as “The Laminate Culture” or “The Lamination People” because of the clothing they produced, saw the end of expansion within the Milky Way before most of the rest of us had. Due to coincidences in the angular momentum of outer-spiral stars, they were hedged in by strong nations in a tense yet stable peace. They needed somewhere to grow, but didn’t dare move in on any of the stars in their neighborhood.
And so they hatched an ingenious yet barmy plan to send colonists to the Andromeda galaxy. They intended to settle those stars with Laminate Culture colonies early, and spread outward through that galaxy before anyone else had managed to start an expedition. To their credit, they thought big and they thought long-term: the journey would take a thousand years, and they’d have no way of ferrying wealth from these new stars to the motherworld. This was a very very long game, and it took a special kind of desperation to even want to play it. --A Blagger's History of Torei