Monoethnicity is the existence of a single ethnic group in a given region or country. It is the opposite of polyethnicity. The use of the concept of monoethnicity has been criticized for being discriminatory and preventing diversity from being recognized.
It is a common belief in Japan that the entire country is monoethnic, but there are many ethnic minorities in Japan (e.g. Koreans, Ainus, and Ryukyuans). They represent around 1% of the whole population
South Koreans regard themselves as a monoethnic society, although there are small ethnic minorities that exist in South Korea, where they account for around 1% of the South Korean population. These include around 650,000 Chinese immigrants
Most Sub-Saharan African countries have mono-racial societies (>0.1%), but it's common to find several ethnic groups within the same country. The number of immigrants from these African countries has grown substantially since 1990, but they receive virtually almost zero immigration.
The Yugoslav Wars are noted as having made territories "de facto monoethnic nation-states".