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After the renegades were expelled from Tarsonis, Kerrigan held another conference with Jim Raynor, Fenix, and Terran Dominion Emperor Arcturus Mengsk (who had been kept in cold sleep until then). Mengsk was very unhappy about his treatment, which only made Kerrigan and Raynor happy. Both of them had had reasons to hate the former commander of the Sons of Korhal, due to his actions during the Fall of Tarsonis, and the two made these reasons well known to Mengsk.
Kerrigan unfroze him because she needed the use of his psi-emitters. Mengsk had been frozen for quite some time, and was unaware that the UED had found and activated the Psi Disrupter. With his emitters, Kerrigan would have the means to gather enough Zerg to destroy the Psi Disrupter and confront the UED. In return for Mengsk's cooperation, she offered to help him retake Korhal, his throne world, which at that point was under UED occupation.
Mengsk wanted to know how he could trust her, and she responded that if he didn't cooperate, he could remain Emperor of an eight by eight cell for the rest of his life. Mengsk was "persuaded" to join Kerrigan's alliance by this kind of talk.
Jim Raynor and his Raiders descended upon Braxis, home of the Psi Disrupter and a number of UED troops. Raynor's forces, including ghosts and siege tanks, destroyed the poorly defended fusion reactors powering the Psi Disrupter.
The Psi Disrupter sat on a well-defended hilltop, but was inactive at that moment with the generators destroyed. As Raynor's forces retreated, Mengsk sent down an SCV carrying a psi-emitter to the surface of Braxis. The SCV pilot quickly found a small number of uncontrolled zerg which the UED allowed to roam the world. The psi-emitter attracted the zerg, enabling Kerrigan to take control of them. The SCV pilot roped in drones (capable of constructing a hive cluster), zerglings, hydralisks, and even special zerg breeds (the Devouring One, a powerful zergling strain, the Hunter Killer, a powerful hydralisk strain, and the Torrasque, a powerful ultralisk), tangling with UED outposts along the way. When these zerg had all been added to Kerrigan's Swarm, the SCV requested and gratefully received transport away from the zerg.
Kerrigan quickly built up a strong force and attacked the UED base built around the Psi Disrupter. Despite the well-designed UED defenses, the Zerg Swarm defeated them and destroyed the Psi Disrupter.