This hugely escalated the war and also made allies of the most powerful capitalist countries and the most powerful communist one an alliance that would stand the test of time and never end until like three seconds after the defeat of the Nazis. The Nazi invasion of Russia opened the war up on the so-called Eastern Front, although if you were Russian it was the Western Front, and it led to millions of deaths, mostly Russian. Also, 1941 saw a day that would live in infamy when the Japanese bombed Pearl Harbor, hoping that such an audacious attack would brighten the United States into staying neutral, which was a pretty stupid gamble because 1. the US was already giving massive aid to the Allies and was hardly neutral, and 2. the United States is not exactly famed for its pacifism or political neutrality. 1941 also saw Japan invading much of Southeast Asia, which made Australia and New Zealand understandably nervous. As part of the British Commonwealth, they were already involved in the war, but now they could fight the Japanese closer to home. And shut up about how I never talk about you Australians, I just gave you 1.5 sentences. But by the time the Americans and Australians started fighting the Japanese, it was already a world war.