Four distinct periods can be distinguished. The first part of the beginning of war in Europe in September 1939, at the end of the "phoney war", in which the Allies and the Axis powers intercepted neutral merchant ships to enter cargo for the enemy. The second period began after the rapid occupation by the Germans of the majority of European countries which gave him control of large industrial centers and agricultural areas. The third period ran from the end of 1941, beginning of hostilities between America and Japan, until the end of 1942. The latter period came after the reflux experienced by Germany following heavy defeats soldiers before and after the Normandy landings, leading to a gradual withdrawal from the occupied territories face of
