The Combine's first appearance is in Half-Life 2. Through the early stages of the game, Combine Civil Protection units pursue Gordon Freeman through City 17 after his presence is revealed to Wallace Breen. Due to Freeman's actions in Half-Life, Breen sees Freeman as a major threat. As Freeman flees the city, Civil Protection units raid the resistance base of Black Mesa East and capture resistance leader Eli Vance, who is transferred to holding facilities at Nova Prospekt. Freeman and Vance's daughter Alyx break into the facility to rescue him, but Eli is teleported to the Combine Citadel by double agent Judith Mossman. The strike against Nova Prospekt prompts a revolution by the citizens of Earth and heavy street fighting takes place. Freeman battles Combine Overwatch to infiltrate the Citadel but is captured and taken to Breen. With suppressing the revolution failing, Breen flees to the Citadel's trans-dimensional teleporter to escape. Freeman destroys the teleporter's reactor before Breen can flee, causing a large explosion that destroys the top of the Citadel.
