The Second Polish Republic, at the time officially known as the Republic of Poland, was a country in Central and Eastern Europe that existed between 7 October 1918 and 6 October 1939. The state was established in the final stage of World War I. The Second Republic ceased to exist in 1939, after Poland was invaded by Nazi Germany, the Soviet Union, and the Slovak Republic, marking the beginning of the European theatre of the Second World War. The Polish government-in-exile was established in Paris and later London after the fall of France in 1940.

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.