The U. S. supported Ngo Dinh Diem because he was

President Eisenhower approves a National Security Council paper titled "Review of U. S. Policy in the Far East." This paper supported Secretary of State Dulles' view that the United States should support Vietnamese prime minister Ngo Dinh Diem, while encouraging him to broaden his government and establish more democratic institutions. Ultimately, however, Diem would refuse to make any meaningful concessions or institute any significant new reforms and U. S. support was withdrawn. Diem was subsequently assassinated during a coup by opposition generals on November 2, 1963.