Kuiper Belt

The Kuiper Belt, known by most as just "The Belt" is a largely ungoverned part of the Sol System, located between Mars and Jupiter. This region consists entirely of a large asteroid belt, dotted by multitudes of various mining colonies, gang hideouts, homesteads, and upstart countries or "Astrostates".

History
After Humankind invented techniques to easily terraform and colonize worlds, most of the prime real estate, e.g. planets were taken, forcing people to go to the asteroid belt to make a living. Most of it is mining territory, although some parts are used for shady bars and discotheques. Many an upstart warlord has swooped in, capitalizing on the lack of Union control.