4. Ngo Dinh Diem
Serving as the final prime minister of the State of Vietnam (1954–55), and then serving as President of South Vietnam (Republic of Vietnam) from 1955, Ngo Dinh Diem’s days were numbered when he began persecuting South Vietnam’s Buddhist majority. The violence lost him not only the support of the United States but saw him lose the favor with the leadership of the Army of the Republic of Vietnam.
Although he had formerly supported Diem, President John F. Kennedy would authorize the CIA to assist the country’s leading generals in overthrowing Diem’s government in a coup d’état. Diem and his brother Nhu initially escaped but were captured the following day, and both were shot to death in an armored car. His assassination would directly lead to more American troops entering Vietnam.