December 1941: The Tide of War Turns

On September 1, 1939, Hitler invaded Poland, launching the Second World War in Europe. Across the Atlantic, the United States showed no appetite for getting involved in the European conflict. For two years, the United States maintained its policy of non-intervention, although they did provide material assistance to the Allied forces facing Hitler's armies. Then came December 7, 1941. It can be argued that the events of that day and those that followed made December of 1941 the most momentous month of World War II.

Japan Pushes the United States

USS Arizona (BB-39) explodes during the attack on Pearl Harbor, 7 December 1941

On the morning of December 7, 1941, the United States was still officially a neutral party to the war raging in Europe. Supplies and other non-combat support were being provided to the United Kingdom, but there was no explicit plan to send fighting forces, despite Prime Minister Winston Churchill’s pleas.

The British may not have been able to drag the United States into combat, but an unexpected third party did just that. In response to failed negotiations with the United States, Japan launched an assault on the Pearl Harbor Naval Base on Oahu, killing 2,403 Americans and causing enormous damage to the US Pacific Fleet.

It was on this day that the course of World War II would change. First, it launched the War in the Pacific, a brutal four-year conflict largely fought between the United States and Japan. With Japan’s focus now to the east, the Soviet Union was able to shift divisions from the Siberian border to aid in the defense of Moscow. Relations between the Soviet Union and Japan had been tense leading up to the Pearl Harbor attack, but it was clear from the beginning that Japanese officials would not be looking to fight a two-front war.

The Allies Get Some Help

Axis powers declare war on the United States, 11 December 1941

Up until December of 1941, the Soviet Union had been relying on Britain as an ally on the western front of the European war. Germany had so far proven powerful enough to fight back both armies, earning decisive early victories that put the war in Hitler’s favor.

When Japan launched its attack on the United States, the Americans immediately declared war against the attackers, triggering the mutual defense clause of the Tripartite Pact between Germany, Italy, and Japan. Hitler now had no choice but to declare war on the United States. America's longstanding policy of isolationism was officially dead.

December 1941:The Most Significant Month of the War

Over the course of four days, December, 1941 became a pivotal time in World War II. It was in this month that the Allies began to receive desperately-needed assistance in Europe, and new theater of the war was launched. Without US involvement, the war might have had a very different outcome. Japan may have continued taking over territories in China and Southeast Asia, and Hitler’s forces may have been able to seize even more of Europe.