Despite his initial military successes, his unrealistic appraisals led him repeatedly to override his own generals and ultimately to cause Germany’s defeat. Those fatally unrealistic decisions included his unprovoked declaration of war against the U.S. in December 1941 at a time when Germany was already at war with Britain and the Soviet Union, and his overriding of his generals’ pleas to authorize retreat by the German army trapped at Stalingrad in 1942–1943.