Peacekeepers are predominantly Sebaceans. The Peacekeepers are by all definitions an organization of mercenary soldiers. At one time they merely exercised dominion over their own species but they soon realized they could be much more. In time they  expanded their  power and control into many other sectors. They now sell their services to other planets and races that do not have a military force. They also have become a major force in "law enforcement" and as such many of the planets they serve have turned over many of their prisoners for the Peacekeepers to deal with. Peacekeepers are tenacious fighters with massive ships and overwhelming weaponry.