In May-June the rapidly advancing tank forces defeated France and the Low Countries.

The major goal of Hitler's conquest lay in the East, however, and already in the middle of 1940 German war production was preparing for an eastern campaign. The Air Battle of Britain, which Hitler had hoped would permit either German invasion or (this continued to be his dream) an alliance with "Germanic" England, was broken off, and Germany's naval operations collapsed for lack of reinforcements and materiel.

On June 22, 1941, the German army advanced on Russia in the so-called Operation Barbarossa, which Hitler regarded as Germany's final struggle for existence and "living space" (Lebensraum) and for the creation of the "new order" of German racial domination. After initial rapid advances, the German troops were stopped by the severe Russian winter, however, and failed to reach any of their three major goals: Leningrad, Moscow, and Stalingrad. The following year's advances were again slower than expected, and with the first major setback at Stalingrad (1943) the long retreat from Russia began. A year later, the Western Allies, too, started advancing on Germany.

With the waning fortunes of the German war effort, Hitler withdrew almost entirely from the public; his orders became increasingly erratic and pedantic; and recalling his earlier triumphs over the generals, he refused to listen to advice from his military counselors. He dreamed of miracle bombs and suspected treason everywhere. Under the slogan of "total victory or total ruin," the entire German nation from young boys to old men, often barely equipped or trained, was mobilized and sent to the front. After an unsuccessful assassination attempt by a group of former leading politicians and military men on July 20, 1944, the regime of terror further tightened.

In the last days of the Third Reich, with the Russian troops in the suburbs of Berlin, Hitler entered into a last stage of desperation in his underground bunker in Berlin. He ordered Germany destroyed since it was not worthy of him; he expelled his trusted lieutenants Himmler and Goring from the party; and made a last, theatrical appeal to the German nation. Adolf Hitler committed suicide on April 30, 1945, leaving the last bits of unconquered German territory to the administration of non-Nazi Adm. Karl Doenitz. .