From the introduction: Welcome, possibly once more, to the Koprulu Sector. It is here that three might races find themselves in a near perpetual state of combat. The Terrans; once humans of earth but lost adrift in space centuries ago until they arrived here. The Protoss; an ancient race made up entirely of potent psionic users and even more potent psionic technology. The Zerg; an all consuming swarm, made up of countless critters bound under a hivemind.