On December 7, 1941, the Japanese attacked Pearl Harbor and started a war with the United States. The wisdom of that decision was itself dubious, but the mistake made by Adolf Hitler a few days later easily equaled it in dire consequences. It had been a good year for Hitler and the Third Reich. The German army had conquered most of Europe and the only setbacks had seemed minor. The British had managed to repel the air offensive and so avoid an invasion of their island. In Africa, Erwin Rommel had been stopped short of Cairo in what was really a minor sideshow. The war with Russia had gone brilliantly with almost 2 million Russian soldiers killed or captured and vital parts of that country occupied. For years, Hitler had cultivated the Japanese leadership in expectation that Japan would attack Siberia, providing a second front against Russia. The German foreign minister, since Operation Barbarossa, had suggested to Japan that mineral-rich Siberia was theirs for the taking. Hitler personally had seen the damage having to fight on two fronts did in World War I to Germany. He was anxious for Russia to suffer the same fate.
When Adolf Hitler heard about Pearl Harbor, he was recorded as being visibly happy. Based on what he did next, there must have been an expectation that Japan, who had already declared themselves an ally of Germany and Italy, would join in attacking Russia. What he did not know was that months earlier the Japanese had decided to concentrate on the United States and had no interest in attacking Russia. Worse for Germany was the fact that Russia had been informed of this by a spy in Tokyo. This security breach served both Japan and Russia well. It allowed Stalin to begin pulling the elite Siberian battalions west immediately after the Germans invaded. With most of the Russian divisions gone, Japan did not need to station significant forces on the Russian border either. By October 1941, the Russians and Japanese had actually signed a nonaggression pact. The loser was Germany. But four days after Pearl Harbor, on December 11, Adolf Hitler declared war on the United States in support of Japan. That he did so based on a false assumption is clear from his remarks at the time. He expected Japan to attack Russia. Also, after seeing the effect American units had when they finally joined in the Great War, he certainly wasn’t anxious to see them in Europe again. It was his expectation that Japan would distract America, leaving Germany free to complete what seemed to be the inevitable conquest of Russia and to force a peace on Britain. Of course that was not how it worked.
But there was another factor beyond unrealistic expectations that made this declaration one of the worst mistakes the German Führer ever made. The American public simply did not want to get involved in a second war. Isolationist candidates had won many elections. For more than two years the American president, Franklin Roosevelt, had been lobbying for the country to be more involved in the war in Europe. His often-stated opinion was that if the Nazis were able to use the wealth and manufacturing power of an occupied Europe, they would pose a deadly threat next to the Americas. But on December 10, 1941, the Americans were not angry with Germany. On December 8, Congress had declared war only on Japan. The military, and the people, wanted revenge for that day of infamy. But by declaring war on December 11, Hitler made Germany appear part of the conspiracy. It gave Roosevelt an opening to do what he wanted, where he wanted. Only after Hitler declared war was the American declaration expanded to include Germany. Almost immediately, the power generated by the surprise attack was channeled into Roosevelt’s Europe First policy. America began to mobilize and plans were made to send the bulk of the new army to England, not the Pacific. The shipments of trucks and weapons to all of the European Allies were dramatically increased as the United States went on a wartime footing.
It is likely that eventually the United States would have joined the war in Europe. But without Hitler’s declaring war first this might have happened months later. The Asia First movement was strong even after Hitler’s declaration. It is notable that, in his December 9 fireside chat, Roosevelt did not call for a declaration of war on Germany. He blamed them for having goaded Japan into attacking but stopped short of widening the war. Had he done so, he might well have lost the amazing unity caused by Pearl Harbor and become more susceptible to the growing attacks he was under for his failed domestic policies. So without Hitler doing it for him, Roosevelt would likely have had to wait months before declaring war on Germany, perhaps longer. Those months of delay could have been decisive. In a scenario that does not include the massive number of trucks, tanks, aircraft, weapons, and ammunition that the United States sent to Russia and England during those months, the German army might well have been victorious in Russia in 1942. Without the American armed forces in Europe and a resilient Russia, the defeat of Germany, if possible at all, would have taken years longer.
Rarely has a wartime leader been so completely wrong. In declaring war on the United States on December 11, Hitler accomplished exactly the opposite of what he expected. It gained Germany no assistance against Russia and enabled Roosevelt to shift the emphasis of the American war effort to Europe. Hitler’s declaration of war may have actually served Japan well, but only because it allowed Roosevelt to send fewer forces to the Pacific and more forces to Europe. An emphasis on Japan would have meant that the war in the Pacific would have ended earlier. Instead, by declaring war on the United States at a crucial time when American anger was just crystallizing, that Nazi act of solidarity helped both to hasten and to make inevitable the defeat of Germany.