World War II was a global conflict that lasted from 1939 to 1945, involving many 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, the Soviet Union, and the United Kingdom. The war resulted in significant changes to the world map and led to the establishment of the United Nations in 1945 to promote peace. It also caused immense destruction and loss of life, with millions of people affected by battles, bombings, and the Holocaust, where six million Jews were killed.