Unified World

The Unified World is a fusion of Sonic's World and Earth 20XX, the creation of which was brought about by the Maverick Reploid Sigma in his attempt to drain them of its life force.

The world contains all of the locales of both Sonic's World and Earth 20XX meshed together and overlapping. Since the world was created during the time Sonic's World was experiencing the Shattered World Crisis, the entire planet was split apart.