In 1945, the world was marked by the end of World War II, a conflict that lasted six years and involved many nations. The war concluded in Europe with the unconditional surrender of Nazi Germany in May, followed by the surrender of Japan in September after the United States dropped atomic bombs on the cities of Hiroshima and Nagasaki. The aftermath of the war led to significant geopolitical changes, including the establishment of the United Nations in October to promote international cooperation and prevent future conflicts. The year also saw the beginning of the Cold War, as tensions rose between the United States and the Soviet Union.