Why was Ngo Dinh Diem overthrown and killed in 1963?

Ngo Dinh Diem was overthrown and killed in a November 1963 coup d’état primarily due to his increasingly autocratic rule, the failure of his government to effectively counter the Viet Cong insurgency, and his alienation of the South Vietnamese populace.123

Key factors contributing to his downfall included:

• Religious Conflict: As a Roman Catholic, Diem’s favoritism toward fellow Catholics alienated the Buddhist majority. Tensions escalated in 1963 following violent government crackdowns on Buddhist protests, which included the self-immolation of monks and a nun.243
• Ineffective Governance: Diem’s regime was characterized by corruption, nepotism, and the use of totalitarian methods against political opponents. His failure to implement promised land reforms and the unpopularity of the Strategic Hamlet Program further weakened his support.243
• Loss of U.S. Support: Following the public outcry over the repression of Buddhists, the United States withdrew its backing. After South Vietnamese generals secretly consulted with U.S. officials regarding a potential coup, the U.S. embassy maintained a neutral stance, effectively signaling that it would not intervene to save the Diem administration.245

On November 1, 1963, military units seized control of Saigon and occupied the presidential palace, leading to the deaths of Diem and his brother, Ngo Dinh Nhu.453