Since the formation of the league of nations in 1920 as a result of the Paris Peace Conference that ended the First World War. The Big Five has been the decision makers of the world politics.
Though they crashed the league of nations on April 20, 1946, after it failed to prevent the second world war and that ushered in the United Nations, with the primary purpose to preventing the Third world War, promote international cooperation and to create and maintain international order.
After the formation of United Nations, the five allies during the war (China, France, Russia, the United Kingdom, and the United States.) calved out permanent seats for themselves at the Security Council. Ever since they have been in control of the world.
What have United nations done for the world? Just take a look at Syria, Iraq, Afghan and other countries. Even The World Health Organization an agency of the United Nations that is concerned with international public health since it establishment on 7 April 1948, have not been able to provide a cure for common diseases - Cancer, Malaria and HIV/AIDS. Millions of dollars are spent annually for medical research still they can't boast of any meaningful cure.
United Nations has become a club rather than an agency. More than 60% of it budgets goes into an administrative cost. Russia took over crimea, China building Man-made island in the disputed border, France - Germany, and UK suffering from immigration nightmare... The United States fighting identity politics. They have all failed.