The global event that took place from 1939 to 1945 was World War II. This massive conflict involved most of the world's nations and was marked by significant events, including the Holocaust, the use of atomic weapons, and widespread military engagements across Europe, Asia, and Africa. The war began with Germany's invasion of Poland in September 1939, leading to the Allied powers, including the United States, the Soviet Union, and Great Britain, opposing the Axis powers led by Germany, Italy, and Japan. The war ended in Europe with Germany's unconditional surrender in May 1945 and in Asia with Japan's surrender in September 1945.