The most powerful entity within the United Nations is:

The most powerful entity within the United Nations is the Security Council. The Security Council is responsible for maintaining international peace and security and has the authority to impose sanctions, authorize the use of force, and make binding decisions on member states. It consists of fifteen members, including five permanent members with veto power (China, France, Russia, the United Kingdom, and the United States) and ten non-permanent members elected for two-year terms.