[pm3003]

Probably Georgia as a political entity, Armenia, Cambodia and Vietnam as nations probably.

I know other examples of relative ethnic stability: most of Northern Europe broadly has the same ethnic geographic boundaries as 1500 years ago (excepting the slavic / proto slavic things), the Basque, the Sardinians, Bretons and Bearnese, Tirolians, Kabyles, Laz "Greeks" (vanishing since WWII).

By some measures also Egypt (coastal cities excepted) and Iran.