Harry S. Truman played a critical role in the establishment of the United Nations (UN) after World War II. As the President of the United States from 1945 to 1953, Truman recognized the need for international cooperation to ensure peace and prevent future conflicts. He was instrumental in promoting the UN's founding principles, particularly the importance of diplomacy and dialogue among nations. Truman's commitment to the UN was evident during the formation of its charter in 1945, where he emphasized human rights and the need for collective security. His vision helped shape the UN into a platform for global cooperation and conflict resolution.