Between 1938 and 1945, Nazi Germany occupied or controlled vast territories of Europe. Peaking in 1941–1942, Germany and the other Axis powers were governing more than half of the entire continent's population through direct administration, civil occupation, and military occupation, as well as by establishing puppet states. Germany's expansionist campaigns under the Nazi Party of Adolf Hitler ultimately led to the beginning of World War II in 1939. Also inside some of these occupied states, particularly Poland, was a large network of Nazi camps that facilitated what would later become known as the Holocaust.