The Atlantic Charter, established in 1941, was a pivotal agreement between the United States and the United Kingdom, shaping post-war plans during World War II. It emphasized principles like self-determination, economic cooperation, and disarmament, laying the groundwork for future international organizations such as the United Nations. The Charter united the Allies in their fight against tyranny and provided a vision for a peaceful world order post-war, marking a significant shift in U.S. foreign policy toward greater involvement in global affairs.