The Cold War “containment" notion was born of the Domino Theory, which held that if one country fell under communist influence or control, its neighboring countries would soon follow. Containment was the cornerstone of the Truman Doctrine as defined by a Truman speech on March 12, 1947. The Truman Doctrine, the Marshall Plan, NATO and the United Nations then became the foundation of American foreign policy through the Reagan administration and beyond, for about 50 years.