The war in the Pacific continued after Germany's surrender, and the final battles there were among the hardest fought. Beginning in June 1944, the Battle of the Philippine Sea wreaked havoc on the Japanese Navy, forcing the resignation of Japanese Prime Minister Tojo. General Douglas MacArthur -- who had reluctantly left the Philippines two years before to escape Japanese capture -- returned to the islands in October, clearing the way for the U.S. Navy. The Battle of Leyte Gulf resulted in a decisive defeat of the Japanese Navy, restoring control of Philippine waters to the Allies.  

By February 1945, U.S. forces had taken Manila. Next, the United States set its sight on the island of Iwo Jima in the Bonin Islands, about halfway between the Marianas Islands and Japan. But the Japanese were determined to hold the island, and made the best use of natural caves and rocky terrain. U.S. bombardment met determined Japanese resistance on land and kamikaze suicide attacks from the sky. U.S. forces took the island by mid-March, but not before losing the lives of some 6,000 U.S. Marines and nearly all the Japanese forces. The U.S. began extensive air attacks on Japanese shipping and airfields. From May through August, the U.S. 20th Air Force launched wave after wave of air attacks against the Japanese home islands.  

The heads of the U.S., British and Soviet governments met at Potsdam, a suburb outside Berlin, from July 17, to August 2, 1945, to discuss operations against Japan, the peace settlement in Europe, and a policy for the future of Germany.  

The conference agreed on the need to assist in the reeducation of a German generation reared under Nazism and to define the broad principles governing the restoration of democratic political life to the country. The conferees also discussed reparations claims against Germany, agreed to the trial of Nazi leaders accused of crimes against humanity, and provided for the removal of industrial plants and property by the Soviet Union. But the Soviet claim, already raised at Yalta, for reparations totaling $10 thousand-million remained a subject of controversy.  

The day before the Potsdam Conference began, an atomic bomb was exploded at Alamogordo, New Mexico, the culmination of three years of intensive research in laboratories across the United States in what was known as the Manhattan Project. President Truman, calculating that an atomic bomb might be used to gain Japan's surrender more quickly and with fewer casualties than an invasion of the mainland, ordered the bomb be used if the Japanese did not surrender by August 3. The Allies issued the Potsdam Declaration on July 26, promising that Japan would neither be destroyed nor enslaved if it surrendered; if Japan did not, however, it would meet "utter destruction." A committee of U.S. military and political officials and scientists considered the question of targets for the new weapon. Truman had written that only military installations should be targeted. Secretary of War Henry L. Stimson, for example, argued successfully that Kyoto, Japan's ancient capital and a repository of many national and religious treasures be taken out of consideration. Hiroshima, a center of war industries and military operations, was chosen.  

On August 6, a U.S. plane, the Enola Gay, dropped an atomic bomb on the city of Hiroshima. On August 8, a second atomic bomb was dropped, this time on Nagasaki. Americans were relieved that the bomb hastened the end of the war; the realization of its awesome destructiveness would come later. On August 14, Japan agreed to the terms set at Potsdam. On September 2, 1945, Japan formally surrendered.  

In November 1945 at Nuremberg, Germany, the criminal trials of Nazi leaders provided for at Potsdam took place. Before a group of distinguished jurists from Britain, France, the Soviet Union and the United States, the Nazis were accused not only of plotting and waging aggressive war but also of violating the laws of war and of humanity in the systematic genocide, known as the Holocaust, of European Jews and other peoples. The trials lasted more than 10 months and resulted in the conviction of all but three of the accused.  

One of the most far-reaching decisions concerning the shape of the postwar world took place on April 25, 1945, with the war in Europe in its final days, although the conflict still raged in the Pacific. Representatives of 50 nations met in San Francisco, California, to erect the framework of the United Nations. The constitution they drafted outlined a world organization in which international differences could be discussed peacefully and common cause made against hunger and disease. In contrast to its rejection of U.S. membership in the League of Nations after World War I, the U.S. Senate promptly ratified the U.N. Charter by an 89 to 2 vote. This action confirmed the end of the spirit of isolationism as a dominating element in American foreign policy and signaled to the world that the United States intended to play a major role in international affairs.