- League of Nations (LON): After World War I, the LON was created to prevent future conflicts and promote international cooperation. However, it was unable to resolve various conflicts and crises effectively, and its authority declined.
- Allies' Meeting in Moscow (1943): During World War II, the United States, the United Kingdom, and the Soviet Union (the Allies) began discussions on establishing a new international organization. They agreed to create an organization to maintain peace and security and emphasized the importance of great power unity.
- Dumbarton Oaks Conference (1944): Further discussions among the Allies took place in Washington, D.C. at Dumbarton Oaks. The Dumbarton Oaks proposals laid out the framework for the UN, including the creation of a Security Council, General Assembly, and International Court of Justice.
- Yalta Conference (1945): The "Big Three" leaders of the Allies - U.S. President Franklin Roosevelt, British Prime Minister Winston Churchill, and Soviet Premier Joseph Stalin - met at Yalta in Crimea to discuss postwar arrangements, including the future UN. The Yalta Conference solidified the plans for the UN and reached agreements on voting procedures and the veto power of the five permanent members of the Security Council.
- San Francisco Conference (1945): The United Nations Conference on International Organization, also known as the San Francisco Conference, convened from April to June 1945 in San Francisco. Delegates from 50 countries met to negotiate and finalize the UN Charter, which embodied the principles and structure of the organization.
- Adoption and Signing of the UN Charter: On June 26, 1945, the UN Charter was signed by the delegates of 51 participating nations. Poland, which was unable to attend the conference due to the ongoing war, signed the charter later, bringing the total number of original signatories to 51.
- Ratification and Entry into Force: The UN Charter required ratification by the governments of the signatory states in accordance with their respective constitutional processes. The charter came into force on October 24, 1945, after being ratified by the required number of states, including all five permanent members of the Security Council.
The formation of the UN after World War II reflected a determination among nations to prevent future conflicts, promote cooperation, and establish a rules-based international order to maintain global peace and security.