The Second World War was a global conflict that lasted from 1939 to 1945, involving most of the world's nations. It began when Germany, led by Adolf Hitler, invaded Poland, prompting Britain and France to declare war. The war saw the rise of the Axis Powers, including Germany, Italy, and Japan, against the Allied Powers, which included the United States, Soviet Union, and United Kingdom. The war resulted in significant changes to the global landscape, including the establishment of the United Nations and the beginning of the Cold War. It was marked by major events such as the Holocaust, the use of atomic bombs on Hiroshima and Nagasaki, and the eventual defeat of the Axis Powers in 1945.