The major international conference in 1945 that established the United Nations was the San Francisco Conference. Held from April to June, this conference was attended by representatives from 50 countries, who aimed to create a new international organization that would promote peace, security, and cooperation among nations in the aftermath of World War II. The conference resulted in the drafting and adoption of the UN Charter, which laid the foundation for the organization's structure and principles. The UN was established on October 24, 1945, marking a significant step toward international diplomacy and collaboration in addressing global challenges.