The policy of involvement in the Vietnam conflict began in the mid-1950s when President Harry S. Truman (1884–1972) provided U.S. support to the French in their struggle to retain control of Vietnam, which was then part of French Indochina. In the Cold War era (1947–89), government leaders believed that the United States must come to the assistance of any country threatened by communism. Truman’s successors in the White House, Presidents Dwight D. Eisenhower (1890–1969), John F. Kennedy (1917–1963), and Lyndon B. Johnson (1908–1973), also followed this school of thought, fearing a “domino effect” among neighboring nations—if one fell, they’d all fall.