Monoethnicity is the existence of a single ethnic group in a given region or country. It is the opposite of polyethnicity. According to the OECD, a country in which 95% of the population is dominated by single ethnicity is a homogenous/monoethnic state.
An example of a largely monoethnic country is Japan. It is a common belief in Japan that the entire country is monoethnic, but a few ethnic minorities live in Japan (e.g. Koreans, Ainus, and Ryukyuans). They represent around 1% of the whole population.[1]
South Korea is another largely monoethnic country. 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.
The Yugoslav Wars are noted as having made Yugoslavia's successor states "de facto and de jure monoethnic nation-states".