The Vigilance was a government with a slave-based economy founded on the moon Titania. It was destroyed by the Centro Systems Military, led by Commodore Cornelia Carthage, in 2451. Remnants of it lingered on after it's official destruction however. They were very bad people. No really, they're bad guys. We know this is a big "shades of grey" setting, but the Vigilance are not nice.
The Vigilance was founded by early Rimward settlers seeking independence from Centro Systems, who discovered that enslaving their neighbors made it easier to survive without Centro support. This was later rationalized into a culture that idolized older slave-holding cultures as a way to justify the horrors they continued to perpetrate on the rest of the Rimwards.
The Vigilance made an incursion into Centro territory in 2434, attempting to raid an undefended Mars for slaves. Commodore Melinda Talon scrambled a fleet of in-repair and drydocked ships in order to repel the attack successfully, for which she was promoted to admiral. The event left Mars afraid, and scarred a young Zhang Han as she had overheard her parents discussing if killing her was better than letting her be taken by the Vigilance.
The Vigilance kept their security locked down in The Citadel, which also housed the most heinous place of entertainment in the solar system: Torture Paradise. The crimes committed there are too awful to be listed on a family friendly wiki. Torture Bots were utilized there.
Centro Colonel Zhang Han led a commando force to infiltrate the Vigilance on Titania and took down it's orbital defenses by infiltrating the Citadel, and coordinating a slave revolt at the same time Commodore Cornelia Carthage began landing Centro Marines on the moon. The downfall of the government was swift, and the higher ups who survived the revolution were tried and hung, including the Patriarch.
Sympathizers, and members who were not on Titania during the revolution, did survive and continue to operate in secret.