Slovakia had been part of the Czechoslovak Republic from 1918 until 1939, but began issuing its own stamps as a separate country called the Republic of Slovakia in 1939. Until the end of World War II, Slovakia continued to issue its own stamps.
The first stamps used exclusively in Slovakia were stamps of the Czechoslovak Republic (inscribed ČESKOSLOVENSKO) with an overprint reading ‘Slovenský štát 1939’ (Slovak State 1939).
Later in 1939, Slovakia finally issued its own brand new stamps. Although a couple early designs were inscribed SLOVENSKÁ POŠTA, the great majority of World War II Slovak postage stamps were inscribed simply SLOVENSKO. (Be careful not to confuse this with the country of Slovenia.)
In 1945, Slovakia rejoined Czechoslovakia, remaining there until its 1992 independence.
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