Having gained independence in 1918, Poland is the opening theater of WWII in 1939. Based on the Ribbentrop-Molotov pact, both Germany and Russia invade Poland and annex large parts of the country. In the German part, Germany establishes Generalgouvernement Polen. Based on the Ribbentrop-Molotov pact, Russia, in 1940, also annexes the Baltic states in the north and parts of Romania in the south. In 1941 Germany invades Russia and occupies the parts of Poland that were annexed by Russia. The area around Bialystok is added to the German Empire, other areas are added to the Generalgouvernement Polen, the Reichskommissariat Ostland and the Reichskommissariat Ukraine. After the defeat of Germany, Poland gains parts of Germany, the parts lost to the Soviet Union in 1939 become part of the Soviet Union. During the war, stamps are used as issued by the different political entities, by which the different parts of Poland are subsequently governed. After the war in 1944/1945, many cities issue local provisionals, general stamp issues are also resumed in 1944.