1. The Cold War: Both the United States and the Soviet Union emerged as superpowers, but with different ideologies. This led to a long "Cold War," which also was the cause of several proxy wars all over the world in the following decades.
2. The creation of the United Nations: The post-war period saw the creation of the League of Nations, created to ensure that a tragedy such as the Holocaust never happened again. The League of Nations became the United Nations.
3. The war changed the global balance of power: Those countries which were victorious became the permanent members of the Security Council (UK, Soviet Union, China, US, France), while the weakening of Europe triggered a process of decolonization in Africa.