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 c2300AD to 2787, the Inner Sphere was divided into five "pie wedges" around a central, roughly circular core: the five Great Houses and the central Terran Hegemony. With the collapse of the Star League and exodus of the Star League Defense Forces from the Inner Sphere, the Great Houses consumed the moribund Hegemony and turned on to each other. Only Terra remained independent under the aegis of neutral interstellar communications agency, ComStar.

During the next 250 years, civilization was hammered from its 28th Century peak down to 21st Century technology on many worlds and to more primitive states on others - and hundreds of worlds had their populations exterminated all together. The cause for this warfare was a matter of feudal succession to the throne of the fallen Star League hence the four wars of this period were called Succession Wars, while the five Great Houses were said to rule Successor States. Despite hundreds of billions of deaths, the first three Succession Wars resulted in little change to the map after the First Succession War split up the Terran Hegemony between the five Houses.

The brief Fourth Succession War (3028-3030) brought a dramatic change when the Lyran Commonwealth and Federated Suns, on opposite sides of the Sphere, united at the expense of the other Successor States' territories. A number of minor nations appeared in the Inner Sphere during or shortly after the Fourth Succession War. 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.