World War II has completely changed world politics. The greatest direct impact that it had was the destruction of the European balance of power. The war broke the economies of the former imperialist powers such as Britain or France, and it made them weaker militarily, with an end to their world superiority and ownership of colonies.
This power gap brought to the fore two superpowers; USA and the Soviet Union. They had great industrial power, nuclear weapons and differences in ideologies, all which ruled the post-war world. Their competition dominated international affairs throughout the decades, as the world was divided into two competing orbits of power with such alliances as NATO and the Warsaw one.
At the same time, the war triggered the Asian and African decolonization. After patripping their share to the Allied cause and seeing how weak Europe was becoming, subject peoples wanted their independence. Exhausted and humiliated colonial powers could no longer afford to maintain empires against world opinion and eventually broke up into many new nation-states.
The Allies created the United Nations in 1945 as they recognized that the League of Nations failed. The UN, created with a view to co-operation and as the bulwark against violence, was built on to become the foundation of multilateral order. Its Security Council system was modeled after the realities of power after the war with permanent veto wielding membership.
Lastly, the horrors of the war saw attempts to develop international law and human rights. The trials at Nuremberg and at Tokyo turned out to regulate personal responsibility for war crimes. This immediately resulted in the Universal Declaration of Human Rights, which integrated human dignity into the world political order.
Conclusion:
World War II changed global politics irreversibly. It wiped out European dominance, fixed the US-Soviet bipolarity that initiated the Cold War, and enhanced decolonization. It created a UN system of multilateralism and started the International human rights law. These changes characterised the contemporary international system.