The Milky Way galaxy was one-hundred thousand light-years wide, and possessed—roughly one billion years before 2546—four hundred and sixty billion, three hundred and eleven million, nine hundred and twenty-two thousand, eight hundred and ten stars.
Circa four billions years ago the galaxy developed to the point where life could safely evolve, though it took two-to-three billion years more before intelligent life first created interstellar empires. If unmolested, any one species could have dominated the galaxy in mere tens of millions of years. Unfortunately, the expansion waves of multiple species collided before any one could claim overwhelming control.
Eventually a galaxy-spanning, multi-species war broke out—the Dawn War. At its conclusion only the Inhibitors remained active, and they focused their efforts on inhibiting the development of interstellar civilisations.
Since their rise, no intelligent life had been allowed to expand significantly beyond their birthworlds, until the rise of humanity.
Unfortunately, humanity's rise was followed quickly by the Greenfly, which ripped apart entire solar systems and seemed unstoppable in its course: the destruction of the entire Milky Way.