In the fictional BattleTech universe, the Inner Sphere is the region of interstellar space surrounding Earth to a radius of roughly 500 light years. The five Successor States, each ruled by an ancient Great House, are the Inner Sphere's dominant power in the setting's "modern" era, although other nations, empires, and independent worlds have ruled parts of the Inner Sphere in the past, and continue to exist. After the fall of the Star League, the Inner Sphere fractured as each of the Great Houses attempted to secure rulership during the Succession Wars.