The global conflict fought between 1939 and 1945 is World War II. Starting with the invasion of Poland by Nazi Germany, this war involved many of the world's nations divided into the Allies and the Axis powers. It was characterized by significant events and battles, including the Holocaust, the Pearl Harbor attack, and the D-Day invasion. The conflict saw advances in military technology and warfare tactics, resulting in vast destruction and loss of life. WWII ended with the unconditional surrender of Germany in May 1945 and Japan in September 1945, leading to profound geopolitical changes and the establishment of the United Nations.