UN is a widely used abbreviation for the United Nations Organisation (UNO).
The United Nations was set up by the colonial powers who sit on the Security Council which was extended to include the atomic states of USA, Britain, France, Russia and China, all of which hold a veto power.
Veto allows these 5 states to over rule any resolution even if the entire world membership of some 300 states in the world, votes for a resolution.
The UN is thus accused of being a dictatorship of nuclear powers and enforcing their will on the rest of the world.