StarCraft II: Wings of Liberty is a science fiction real-time strategy game and the sequel to the original StarCraft. Set four years after the events of Brood War, the game revolves around three species: the Terrans, the Zerg, and the Protoss. The single-player campaign focuses on the Terrans, following Jim Raynor as he leads an insurgent group against the autocratic Terran Dominion. The campaign is non-linear, with players taking missions for money and using those funds to buy additional units and upgrades between missions aboard the battlecruiser Hyperion. The game features competitive multiplayer with a matchmaking ladder system, a map editor for user-created content, and support for three playable races with distinct units and abilities. Wings of Liberty has been free-to-play since November 2017 and was followed by two expansion packs: Heart of the Swarm, focusing on the Zerg, and Legacy of the Void, focusing on the Protoss.