World War II, lasting from 1939 to 1945, was a global conflict triggered by Nazi Germany's invasion of Poland, leading to the formation of two main alliances: the Axis Powers and the Allied Powers. Key battles included Stalingrad and Berlin, and the war concluded with Germany's surrender on May 8, 1945, followed by Japan's surrender later that year. The aftermath saw Europe divided into free and communist regions and significant societal changes, including women's increased roles in manufacturing.