StarCraft: Brood War — the game takes place in the 26th century. In a region of the Milky Way remote from Earth — the Koprulu sector — there was an interstellar state of Terrans (descendants of the people of Earth exiled from their home planet for various crimes) — the Confederation. The plot of the original StarCraft tells of a war between the Protoss and the Zerg, in which the Terrans were also drawn into it. The war ended with the death of the zerg lord Overmind on the protoss home planet of Aiur.
Two days after the end of StarCraft, the events of Brood War begin. Without the Overmind, power over the zerg fell to a few cerebrals who decided to restore power over the entire Swarm. Following the discovery of the existence of alien life in the Koprulu sector, the United Earth Directorate (UED) decides to send an expeditionary force there to eliminate a potential threat to Earth.