Inner Sphere

In the BattleTech universe, the Inner Sphere is a region of interstellar space surrounding Earth to a radius of roughly 500 light-years, generally demarcated by the outer borders of the "Successor States." Within this region of about 2 million stars, there are approximately 2000 inhabited, habitable planets. Beyond the Inner Sphere is the Periphery.

From 2787 to 3028, the Inner Sphere was divided into five "pie wedges" centered on neutral Terra by the five Great Houses (each of which dominates one of the "Successor States".) During this period, these super powers warred over control of the Inner Sphere and succession to the throne of the fallen Star League in what became known as the Succession Wars. After 3028, a number of minor nations appeared in the Inner Sphere and in 3050, the Clans - lost scions of the Star League - returned to conquer a wedge of the Inner Sphere.

The Periphery surrounding the Inner Sphere is home to a few nations of moderate power and many independent worlds cut off from civilization with the collapse of the Star League. The Inner Sphere perceives the Periphery much like modern developed nations perceive the Third World, though some of the major Periphery nations compare well with the weaker Inner Sphere states.

Beyond the Periphery is unexplored space (sometimes called the Deep Periphery). The Clans exist in a small islet of settled worlds in the Deep Periphery.