Operation Barbarossa, the German assault on Russia, had been scheduled for May 15 (1941) but was delayed by the invasion of Yugoslavia on April 6. Yugoslavia capitulated eleven days later and joined the Tripartite Pact of Germany, Italy and Japan. Seemingly just a quick blitzkrieg, this move nonetheless caused a six-week delay in Hitler’s invasion schedule that would have large implications as the Russian campaign unfolded. On June 22, three million mechanized German troops, including thousands of tanks and planes, launched a massive, three-pronged attack against Russia. The military experts in London and Washington predicted that Russia would be conquered in three months, followed by another invasion attempt against Britain in early 1942 and a ferocious fight over control of the Atlantic Ocean.
Despite the Neutrality Pact he had made with Japan several months before the German invasion, Stalin was still worried about the possibility of a Japanese attack on Siberia. It was acknowledged in the Kremlin in the first days and weeks of Barbarossa that a two-front war against Germany in the west and Japan in the east would be catastrophic. Stalin had been overjoyed with the Neutrality Pact, and he made the unprecedented move to see Japanese Foreign Minister Matsuoka off at the Moscow train station. Whether that agreement would hold in the face of the German invasion remained to be seen.
Hitler’s invasion of Russia turned a potentially powerful ally into a deadly enemy that would sap the strength of his army. After failing to conquer Great Britain in 1940, the Russian invasion in 1941 committed Germany to a two-front war. The best Hitler could hope for on his western front was the delay of another invasion attempt of Britain until 1942, and that assumed victory over Russia in 1941. In 1942 Hitler would be attempting to invade a Great Britain made stronger by increased aid from the United States, and even the possible entry of the United States into the war.
The Nazi blitzkrieg into Russia had moved five hundred miles in seven weeks and was only a hundred miles from Moscow by the beginning of August. The same Allied military minds were still holding to their estimate that Russia would be defeated by October, but in fact the German attack had been slowed substantially by the end of July. Hitler had been second-guessing the tactics of his generals on the battlefield, and this was beginning to show. A failure in Russia would mean the German army would be bogged down on a two-thousand-mile front in winter while the homeland would be under air attack from British air forces, then heavily supplemented by US aircraft. Had the invasion of Russia taken place on the original date of May 15 the German army presumably would have penetrated deeper into Russia before the weather closed in. The Battle of Moscow could have had a different outcome.
Former corporal Adolf Hitler, decorated for his valorous service on the front lines of the Great War, believed he knew more about waging war than the Prussian generals. His successes as an infantryman, terrorist, diplomatic bully, and military victor in early 1940 had made him supremely confident. In reality, he was out of his depth. He already had failed to easily capture the British Expeditionary Force at Dunkirk in May, 1940, and failed again a few months later in the Battle of Britain despite superior air power. Understanding the enormous potential of a comprehensive geopolitical strategy, such as creating a Quadripartite Entente to include Russia in the Tripartite Pact, was beyond his narrow capabilities and destroyed by his hatreds. While Germany was still powerful, the misjudgments in 1940 and the failure to conquer Russia in 1941 were taking a toll. Largely unrecognized at the time, the odds were beginning to shift away from Hitler.