The key agreement that called for the United States to help European nations rebuild after World War II is the Marshall Plan, officially known as the European Recovery Program. Initiated in 1948 by Secretary of State George Marshall, the plan aimed to provide financial assistance and support for economic recovery in war-torn Europe. It was designed to prevent the spread of communism by fostering political stability and economic growth. Over the course of four years, the U.S. allocated approximately $13 billion to help rebuild infrastructure, boost industry, and stabilize economies across Western Europe, leading to significant recovery and growth in the region.