The (First) Slovak Republic, otherwise known as the Slovak State, was a partially-recognized client state of Nazi Germany which existed between 14 March 1939 and 4 April 1945 in Central Europe. The Slovak part of Czechoslovakia declared independence with German support one day before the German occupation of Bohemia and Moravia. It controlled most of the territory of present day Slovakia, without its current southern parts, which were ceded by Czechoslovakia to Hungary in 1938. It was the first time in history that Slovakia had been a formally independent state. Bratislava was declared the capital city.

The Slovak invasion of Poland occurred during Nazi Germany's invasion of Poland in September 1939. The recently created Slovak Republic joined the attack, and Field Army Bernolák contributed over 50,000 soldiers in three divisions. Since most of the Polish forces were engaged with the German armies, which were more to the north of the southern border, the Slovak invasion met only weak resistance and suffered minimal losses.