How did the war expand in 1941?

In 1941, the war expanded significantly with the German invasion of the Soviet Union in June, known as Operation Barbarossa, which opened the Eastern Front. Additionally, the attack on Pearl Harbor by Japan on December 7 led to the United States formally entering World War II, joining the Allies against the Axis powers. These events marked a crucial turning point, as the conflict spread across multiple continents, involving more nations and intensifying military engagements.