After staging an act of Polish aggression to use as propaganda, German forces invaded Poland on 1 September 1939. As a result, Britain and France then declared war on Germany and World War Two officially began. However, British and French aid to Poland was slow to materialise and the Soviet Union invaded Poland from the west on 17 September 1939.
Having to fight on two fronts and with limited help from the Allied nations, Polish forces retreated to neutral Romania. German and Soviet forces took full control over Poland on 6 October 1939 at a cost of 59,000 combined casualties compared to Poland’s 199,700.