Which war was fought by the United States during the 1900s?

World War II was a significant global conflict that the United States participated in from 1941 to 1945, after the attack on Pearl Harbor. This war involved various nations from around the world and was marked by major events such as the Holocaust, the use of atomic bombs on Hiroshima and Nagasaki, and significant battles across multiple theaters including Europe and the Pacific. The involvement of the United States played a crucial role in the Allied victory against the Axis powers, which included Germany, Italy, and Japan. The outcomes of World War II had profound effects on international relations and established the U.S. as a leading superpower in the post-war world.