How did the world changed after World War II ?

Germany surrendered on May 7, 1945, ending the war in Europe. The war in the Pacific did not end until after the U.S. dropped two atomic bombs on Japan — the only time such bombs were ever used in war. Japan surrendered on August 14, 1945.
President Franklin D. Roosevelt, who had led the U.S. in wartime, did not live to see peace. But in a speech written but never delivered, he spoke of the need to preserve peace: "Today we are faced with the preeminent [above all other] fact that, if civilization is to survive, we must cultivate the science of human relationships — the ability of all peoples, of all kinds, to live together and work together in the same world, at peace."