Usually considered the start of the Second World War, the German invasion of Poland,code named Case White, began on 1 September 1939 after Germany had staged a Polish attack. At the orders of Adolf Hitler, had been planned by the Army General Staff (OKH) with relatively little involvement from the Oberkommando der Wehrmacht (OKW).
The campaign, which ended on 6 October, split Poland into three zones:
Under the Army headquarters, headed by Field Marshal Walther von Brauchtisch, the main staff planner was Gen. Johannes Blaskowitz, who commanded the 8th Army in the invasion, part of Army Group South. German and allied forces were:
SS Einsatzgruppen followed the Army forces, although without as genocidal a mandate as they would have in the Russian campaign.
This was the first large-scale use of blitzkrieg operational techniques, with a deep-penetrating corps under Heinz Guderian.
While France and Britain had pledged to support Poland, neither country could have intervened directly into Poland. France, however, could have struck into German,y, with an approximately 5 to 1 numerical superiority in ground tropps.