The Blitzkrieg (lighting war) strategy was first created in the early 20th century. It was not employed in WWI because no suitable tank units were available. The first successful application if this war theory was the German invasion of Poland in 1939. However the best known Blitzkrieg campaign in history was the attack on France by the German Wehrmacht in 1940 which proved the superiority of this strategy masterfully applied by the German general staff. The attack started on 10 May and already finished 22 June. In just 44 days the German battle force broke the Maginot line – a nearly perfect system of fortifications - and defeated the French Army – considered one of the best of that time.