Expulsion from the Slovak state. In 1939, 17,000 Czechs had to leave it
Immediately after the proclamation of the Protectorate of Bohemia and Moravia on 16 March 1939, the government of the new independent Slovak state issued a decree that the authorities should dismiss all replaceable Czechs from their jobs. That year, 17,000 Czechs had to leave the country with their families. The paramilitary organisation Hlinka’s Guard actively and often violently helped in this. This greatly damaged relations between Czechs and Slovaks, but it also created the myth that all Czechs had to leave.
Source https://radiozurnal.rozhlas.cz/slovensko-1939