StarCraft II: Heart of the Swarm is an expansion pack to the military science fiction real-time strategy game StarCraft II: Wings of Liberty and the second part of the StarCraft II trilogy developed by Blizzard Entertainment with the final part being Legacy of the Void. The game was released on March 12 2013. The expansion includes additional units and multiplayer changes from Wings of Liberty as well as a continuing campaign focusing on the Zerg race and following Sarah Kerrigan in her effort to regain control of the swarm and exact her revenge on the Terran Dominion's emperor Arcturus Mengsk.