Galactic federation

"There is no great empire that rules the galaxy. That is a complete fantasy. There are very strong local powers and associations of power, often established through trade unions or governing bodies that oversee trade routes. But immense empires that govern vast regions simply do not work, for there is no way to maintain control over the course of time, and there are too many challenges to disrupt a structure of this size. Yet there are empires that contain dozens of planets, star systems and so forth. This is considered fairly large, particularly in your local environment."(Marshall Vian Summers. Life in the Universe, Chapter 3: The Limits of Space Travel)