Amazon: For Americans, World War II began in December 1941, with the bombing of Pearl Harbor; but for Europe, the war began on September 1, 1939, when Hitler’s soldiers invaded Poland, followed later that month by Stalin’s Red Army. The conflict that ensued saw the debut of many of the features that would come to define the later war—blitzkrieg, the targeting of civilians, ethnic cleansing, and indiscriminate aerial bombing—yet it is routinely overlooked by historians.