President who resigned during the fall of saigon

Explanation:

Nguyễn Văn Thiệu served as president of South Vietnam from 1965 to 1975.

The United States had been assisting the South Vietnamese in the attempt to battle communist forces from North Vietnam as well as those within South Vietnam (the Viet Cong).  But the US eventually gave up the fight and withdrew its forces from Vietnam in 1973.  By 1975, South Vietnam was running out of strength.   Nguyễn Văn Thiệu resigned as president on April 21, 1975.  Saigon, the capital of South Vietnam, fell to the North Vietnamese communist forces by April 30, and South Vietnam unconditionally surrendered to North Vietnam.

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