With the closing months of this year, 2013, we are starting to relive the tumultuous 1960s — the decade that changed America — through 50th anniversaries of key events. Just recently we remembered Martin Luther King's "I have a dream" speech, and toward the end of November we will relive the assassination of President John F. Kennedy.

But one important turning point in our history may very well go unobserved.

Fifty years ago this week, on Nov. 1, 1963, a military coup supported by a faction within the Kennedy administration overthrew the South Vietnamese government of Ngo Dinh Diem. Diem was murdered the following day. Many Americans, especially journalists in Saigon, wanted Diem overthrown. Without him, they argued, South Vietnam would prosper as a strong democracy.

Why was this coup so tragic for the United States? Simply put, the collapse of the Diem government paved the way for American combat forces being sent to South Vietnam. The resulting Vietnam War then spawned our culture war between right and left — which, in turn, corrupted, through polarization, the last 50 years of our politics.

America divided into two camps over the Vietnam War.

Among baby boomers, some young men, with the support of their families, accepted personal responsibility to leave home and fight for the rights of strangers in a strange land. But many others, like Bill Clinton and Newt Gingrich, and especially the sons of elite families, refused to serve their country in that war. Rather, they looked around for arguments to oppose the war and justify their personal decision to avoid its dangers and hardships.

As Susan Sontag famously wrote, the Vietnam War was used as the "perfect other" with which to deconstruct American national pride and show up its past as having been flawed and corrosive, thus delegitimizing its traditional elites by questioning their moral authority.

To defend patriotism and our traditional values, President Richard Nixon mobilized the "silent majority." And the country split into two warring subcultures — the educated elite on one side denigrating Merle Haggard's angry "Okies from Muskogee" on the other.

Thanks to momentum from the antiwar movement, those seeking to change America in fundamental ways took over the Democratic Party in 1972. The antiwar vision of America as "progressive," as liberating its culture from stifling traditionalism, still animates the base of that party.

If Diem had not been overthrown so murderously, the course of South Vietnam's resistance to Hanoi's war of conquest would have followed a different and more self-reliant path. Direct American participation would have been less necessary.

In all probability, Diem would have been eased from power by those South Vietnamese nationalists opposed to his inefficient, family-dominated, intolerant administration. But in such a gradual transition of power, the Saigon government would not have collapsed in the villages and hamlets across rural South Vietnam.

It was that collapse of local authority that, more than anything else, gave Hanoi's cadres a free hand among the villagers. Hanoi used the heaven-sent opportunity well to organize a large-scale guerrilla infrastructure.

This collapse of governance thus tipped the balance of forces against Saigon and made inevitable intervention in combat by its foreign allies — the United States, Australia, South Korea and Thailand.

My dad knew Diem well. In 1954 and 1955, as the State Department's director of Southeast Asian Affairs, he had confidently shaped the American policy that supported Diem against both the remnants of French colonial ambitions and the Communists in Hanoi.

In the early evening of Nov. 1, 1963, Dad called me in my freshman dorm room at Harvard to say with a weary voice,"The coup is underway. It looks bad for Diem." Dad had long since seen Diem's weaknesses as a leader, but at the same time had yet to see any immediate successor who promised charismatic authority to offset the Communists' organizational and subversive capabilities.

Filled with foreboding, I went out to kill time by watching a movie. Ironically, it turned out to be "Lawrence of Arabia" — about a Western adviser who respected his clients and believed in their national cause, yet, despite his best efforts, saw it all turn out badly in the end.

Feeling even more morose after the film, I went by the office of the school paper to learn the most recent news from Saigon (no cellphones then). As I walked into the newsroom, the staff was cheering, celebrating: Diem was dead. A Viet Cong flag hung on the wall. It was a premonition of the American fecklessness that was to kill off South Vietnam itself some 12 years later and trigger the rise of our social conservatives in response.

When a similar insouciant arrogance accompanied the Bush administration's announcement that Saddam Hussein had been overthrown, I remembered with foreboding the misplaced joy of those student journalists on Nov. 2, 1963.

Be careful of your dreams, for they may come true. Overthrowing governments plunges countries into confusion and disarray, bringing forth deep mistrust and intractable intrigue. Rarely does it lead to immediate and gratifying coalitions of the willing where the best and wisest step forward to assume with assurance and skill positions of public trust.

Stephen B. Young, of St. Paul, is the former chief of the Village Government Office, Military Assistance Command, South Vietnam. He is global executive director of the Caux Round Table, an international network of business leaders working to promote a moral capitalism.