Twenty years ago this month, Ngo Dinh Diem, then President of American-allied South Vietnam, was assassinated in the wake of a coup d'etat. It was a shot that marked the beginning of America's involvement in the longest, most costly, and least successful war in our history. Of this event, Lyndon B. Johnson wrote in his memoirs, ''The assassination of President Diem had created more problems for the Vietnamese than it had solved. I saw little evidence that men of experience and ability were available in Vietnam, ready to help lead their country.''
The lack of leadership in Saigon led to Johnson's own political demise, constituted the fundamental flaw in the Nixon administration's program to win the war through ''Vietnamization,'' and was a major cause of the collapse of the Saigon government in April 1975.
Now Vietnam is a communist country with the third-largest armed forces in the world. Former United States bases there are key Soviet naval and aviation facilities in the Far East. And so brutal has the repression been of those who either worked for the Saigon government or were neutral that even the most vociferous US antiwar activists have condemned Hanoi for human rights violations.
Those who gain power by assassination nearly always reap a whirlwind. So do their allies. In Vietnam, some five governments rose and fell in the year following Diem's demise. Instability, not improved effectiveness or legitimacy, was the result. In the case of Diem's murder, the US government was widely believed to have tacitly supported the coup. This we did.
The record later revealed that some in the Kennedy administration believed Diem was impervious to American advice and that his increasing repression of Buddhists would alienate the American public and prove counterproductive in the political struggle against the Viet Cong.
The problems posed for and risks to American interests by authoritarian governments and dictators have persisted. It is hard, for example, not to look at our narrow room for maneuver in Central America without a profound sense of deja vu.
In none of the Central American countries with which we are involved does there appear to be effective, legitimate leadership. The junta heads and dictators with whom we are allied seem impervious to American public and congressional concern about human rights violations or the use of ultraright death squads to carry out vendettas against would-be political opponents. US military advisers warn of the dangers of depending on armies in which corruption is rife and promotion depends largely on political connections. And the rest of the world assumes that we have the power to pull strings that we are either too cynical or naive to exercise.
Should we have the option of determining who comes to power in important (to us) countries where leaders only change by sometimes bloody coups?
One lesson from Vietnam, of course, is that coups and assassinations rarely, if ever, make things better. Self-professed leaders waiting in the wings usually turn out no better than those they would replace.
Another equally important lesson is that the United States should avoid overcommitment to governments, and especially causes, even in strategically important or sensitive areas where leadership and integrity are in short supply. The fact that no amount of US backing or troops, or both, has ever made these governments more effective or legitimate is the real lesson of the assassination of Ngo Dinh Diem and of the Vietnam war.
The world has not been a better or safer place as a result of most American involvements in third-world upheavals and insurgencies. And who is to say that we would actually have been worse off by distancing ourselves from Diem - and all who sought to replace him - and sharply limiting (if not ending) our involvement in Vietnam?