A nation-state!?
A nation-state happens when the territory corresponds to a certain ethnic group that has been converted to a nationality. The group must also occupy that specific territory. The United Kingdom is a nation-state because the English ethnicity has been converted to the nationality and the ethnicity also matches up with the territory. The nationality in the U.K. is British and the main language is English, so the main ethnicity or nationality is English or otherwise known as British.