Diem and his family believed casualties could lead to a coup.

Evidence

Diem and his family believed that casualties suffered on offensive operations against the Viet Cong had been a major cause of the abortive coup d’état in November 1960. … They did not want another attempt at a coup, and therefore they did not want the army to suffer casualties on offensive operations. — Neil Sheehan, A Bright Shining Lie, 347

Categorization

• corroborated: 2 independent passages support this claim — Neil Sheehan, A Bright Shining Lie, 347
• XREF: connects to: Widespread foreknowledge of the coup attempt met with deliberate inaction. — Horne, Alistair, A Savage War of Peace- Algeria 1954-1962, 866