The United Provinces of Mobius, informally the Kingdom of Acorn was the largest and most powerful nation on the continent of Segesni. It was a constitutional monarchy where the King held large amounts of power.
It was common to call it the Kingdom of Acorn after the reigning dynasty, and the fact their duchies made up the bulk of the territory.
The Kingdom was one of the many victims of the Great War, and was the last nation to be defeated. The defeat came when Prince Elias Acorn murdered his father, taking his place as King and swearing allegiance to Robotnik.
Since then, the Acorn Kingdom has been sliced into many different zones, and its once beautiful capital has become an industrial wasteland. Elias still maintains authority as a local governor, ruling as King to keep the population pacified.
The Kingdom is notable for the fact Sonic the Hedgehog was born there.
The "United Provinces of Mobius" label is inspired from "the United Kingdom of Britain and Northern Ireland." This is not only due to the Kingdom of Acorn's status as a constitutional monarchy, but as a passive homage to the fact the UK is the world's most pro-Sonic country.