In the early years of the war, the United States was officially neutral. However, President Franklin D. Roosevelt provided military and financial aid to the Allies, especially Great Britain and China. In December 1941, the United States officially entered the war after the Japanese attack on Pearl Harbor.
Americans were united in their determination to defeat Japan and Germany. However, there were some differences of opinion about how to conduct the war. Some Americans advocated for a "Europe First" strategy, while others believed that the United States should focus on defeating Japan first.
After the war, the United States emerged as a global superpower. The country had a dominant role in international affairs, and it played a leading role in establishing the United Nations.