Fifty-nine years ago, Vietnam's Gen. Vo Nguyen Giap rang a death knell for Western colonialism in Asia, masterminding the defeat of France's armed forces at the battle of Dien Bien Phu in northern Vietnam. He later went on to play a crucial role in forcing the U.S. out of Vietnam, burnishing his standing as one of the 20th century's most important military leaders.

But at the time of his death—in a Hanoi military hospital Friday at the age of 102—Gen. Giap was engaged in a fresh battle: This time, to protect Vietnam's fragile...