Military action
The Great Khan was a leader who unified the remaining marauder empires beneath his banner, and declared a war of expansion against all the galaxy. A war of approximately 5 years saw the horde's advances halted and the Great Khan herself assassinated aboard her flagship.
Historians debate whether the United Federation of Nations' task force with the goal of cleaning up the galaxy per say had any effect on the Great Khan's rise to power. What is known for certain is that the Great Khan was a powerful psychic who rose to power from the warrior castes of the marauders and achieved what was once thought impossible. Through a combination of guile, charisma, and military genius, the newly crowned Great Khan had won the respect and loyalty of the remaining Marauder factions. No longer mere raiders, the Great Khan proclaimed to the galaxy her intent of expanding into the galaxy to secure a new empire for herself and her people, even at the cost of the lives that would be consumed in the conflict. While the Great Bulwark project would slow the Great Khan's advance, the federation underestimated the Khan's military shrewdness. While they estimated that the war would be over in under a year, the conflict dragged on for nearly 5 years. The federation would gain the advantage when the khan was ambushed within unclaimed space. A turian-human-Sangheili trap was laid, and the Great Khan was ensnared. When the armada she was commanding was lost in battle against the federal fleet, the Khan and her closest officers fled into hyperspace in a small shuttlecraft. The Great Khan proved to be fallible. The Federation managed to push back the khan and her forces were to their original space. The Great Khan met her demise as she fought to the bitter end, the war ending with her death. The remaining species of the marauders would be allowed to settle on Terran worlds.