The story is set in the future, where humans (called "Terrans") get stuck in a war between two alien species, the "Zerg" and the "Protoss". The Zerg look like monsters, and are all controlled by a very powerful Zerg called the "Overmind". They fly around the universe and invade planets. The Protoss, who have very advanced technology, look for the planets that the Zerg have taken over. When they find a Zerg planet, they burn it so that the Zerg on that planet cannot spread to others. In the original series human protagonist Jim Raynor and several Protoss allies attack and defeat the Overmind. In "Starcraft: Brood War" Jim's ex-partner Sarah Kerrigan uses deceit and trickery to manipulate the Terran and Protoss into helping her take control of the entire Zerg brood, making her the strongest force in the galaxy.