The Combine Empire invades and takes control of Xen, eventually turning the entire planet into a slave race. The Combine uses its usual technique to destroy the Xenians. That is, they hybridize the dominant species of the planet (In Xen's case, the Vortigaunts) with their own technology to create a "Super soldier" that is adapted to Xen's environment and uses powerful Combine technology. This soldier can effectively take over the planet. The Combine also bribe a member of the victim species to act as the "leader" of the planet to encourage other members of the species to conform to Combine demands. In Xen's case, this leader is the Nihilanth (although it is unknown if Nihilanth is a Vortigaunt or not). In Earth's case a few years down the road, the leader is Wallace Breen.



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