The Expanse was a region located in the Tapani sector. Containing many star systems, it was the first area colonized by emmigrants from the Core Worlds. The colonists first settled on the planet Pelagon around 12,720 BBY. Many of the worlds within the Expanse were rich in ore and minerals.
The Tapani Noble Houses were established in the Expanse, and Shey Tapani forged the Tapani Empire which flourished for 6,000 years. By the time of the Galactic Civil War, six of the seven Noble Houses were located within the Expanse, with only House Cadriaan existing outside its border. For centuries, the Tapani sector was controlled by those in the Expanse, generally within the halls of the Great Council on Procopia. The Expanse's power base was eroded with the establishment of the Freeworlds Territory, the rise of the Mining Guild, and the birth of the Galactic Empire.
The population of the Expanse was divided into two social classes—the noble families and the common citizenry. The Expanse was the home to around three hundred and forty-five noble families, who ruled the various Houses and their territories and assets. The common citizenry included the merchants, laborers, manufacturers, and service providers that kept the sector's economy running.