- Declared war on Japan on December 8, 1941, after the Japanese attack on Pearl Harbor.
- Joined the Allies in the war against the Axis powers (Germany, Italy, and Japan).
- Provided significant military, economic, and logistical support to its allies, particularly the United Kingdom, the Soviet Union, and China.
- Led the invasion of Normandy (D-Day) in June 1944, which marked a major turning point in the war in Europe.
- Developed and used the atomic bomb, which led to the surrender of Japan in August 1945.
Soviet Union:
- Invaded Poland in September 1939, along with Germany, starting World War II.
- Signed a non-aggression pact with Germany (Molotov-Ribbentrop Pact), but was invaded by Germany in June 1941 (Operation Barbarossa).
- Fought a massive and prolonged war against Germany on the Eastern Front, enduring significant casualties and devastation.
- Played a crucial role in defeating German forces, particularly at the Battle of Stalingrad and the Battle of Kursk.
United Kingdom:
- Declared war on Germany in September 1939, after the German invasion of Poland.
- Defeated Germany in the Battle of Britain in 1940, preventing a German invasion.
- Provided a base for Allied operations, including the D-Day landings.
- Played a key role in naval operations and the development of radar and other advanced technologies.
Germany:
- Initiated World War II with the invasion of Poland in September 1939.
- Gained control over much of Europe and North Africa through a series of rapid military victories.
- Invaded the Soviet Union in June 1941, opening a massive front and turning the tide of the war.
- Suffered significant defeats in the Battle of Stalingrad, the Battle of Kursk, and the D-Day landings, leading to its eventual defeat.
Japan:
- Invaded China in 1937, starting the Second Sino-Japanese War.
- Attacked the United States at Pearl Harbor in December 1941, leading to the US entry into World War II.
- Occupied large parts of East and Southeast Asia, including Burma, the Philippines, and Indonesia.
- Suffered major naval defeats at the Battle of Midway and the Battle of the Philippine Sea.
- Faced intensified aerial bombing campaigns and ultimately surrendered after the atomic bombings of Hiroshima and Nagasaki.