Star travel has existed for only a few hundred years, yet human colonization efforts have been fairly aggressive until recently. Initially, large colonies were established on any significant world capable of supporting human life. These early colonies have grown to become the ‘Old’ or ‘Inner’ colonies as they tend to be located most closely to Earth. A few of these have populations numbering in the low billions and have nominal independence from Earth.
In reality most worlds are controlled by an interlocking web of corporate interests, although the average citizen still enjoys considerable freedoms on the Inner colonies. Recent terraforming technology is being applied to these colonies to further improve their suitability for human habitation, with the goal of duplicating Earth on as many of these worlds as possible.
The cost of these improvement projects is paid for by the ‘Outer’ colonies. The Outer colonies are primarily the company-owned resource extraction outposts. The wealth from these mining and refining operations are used to fund terraforming of the Inner colonies. This policy has led to a highly civilized, free interior of human space, while the smaller colonies farther from Earth are more tightly controlled and exploited.