Which Allied Country was the last to join WWII?

Franklin D. Roosevelt had come to the conclusion that the United States would not fight in World War II, but after Japan bombed Pearl Harbor on December 7, 1941, the US declared war on Japan and joined the Allied Powers as the final joining nation.

The last Allied country to join World War II was the Soviet Union. They entered the war on June 22, 1941, after being invaded by Nazi Germany in Operation Barbarossa. This invasion marked the beginning of the Eastern Front of World War II. Prior to this, the Soviet Union had signed a non-aggression pact with Germany known as the Molotov-Ribbentrop Pact, but Hitler eventually broke this agreement by launching the invasion. The Soviet Union's entry into the war greatly shifted the balance of power in favor of the Allies and played a crucial role in the eventual defeat of Nazi Germany.