By delving into the conflict's deep crevices, I came upon a wealth of untapped information pointing me in a different direction. (I owed many of those discoveries to Merle Pribbenow, a retired linguist who found and translated a wealth of documents and histories from the opposing side.) These North Vietnamese sources shed extraordinary light on longstanding debates. They showed that North Vietnam controlled the South Vietnamese "resistance" from the beginning, even while Hanoi's propagandists convinced gullible Westerners that it was a purely local movement. They also refuted the widely held view that the South Vietnamese government was reeling militarily at the time of Ngo Dinh Diem's assassination in November 1963.

Other discoveries resulted from investigation into hitherto neglected aspects of the war. No previous historian had looked in detail at what was taking place in the neighboring "dominoes" when Lyndon Johnson made his fateful decision in 1965 to insert American ground troops into the war. In fact, in Thailand, Malaysia, Indonesia, the Philippines, Australia, Taiwan, South Korea and Singapore, anti-Communist leaders were warning that South Vietnam's fall would cause all the Southeast Asian dominoes to fall, and were offering to commit troops to the anti-Communist cause. Suddenly, the domino theory looked far more plausible.

As the huge size of the unexplored territory became apparent to me, a projected single-volume history of the war turned into a trilogy. The first volume, covering 1954 to 1965, took seven years to complete. Titled "Triumph Forsaken," it was promptly termed "revisionist," since it fundamentally challenged the reigning orthodoxy, joining a small number of other books in that category such as Lewis Sorley's "A Better War" and H. R. McMaster's "Dereliction of Duty."

The book showed that Ho Chi Minh was a doctrinaire Communist who, like his Soviet and Chinese allies, adhered to the Marxist-Leninist view that Communists of all nations should collaborate in spreading the world revolution. By the time of Johnson's decision to deploy ground troops into South Vietnam, Ho and his allies were nearing their objective of turning all of Southeast Asia Communist, and they most likely would have succeeded had the United States bailed out. American intervention made possible an anti-Communist coup in Indonesia and the self-devastation of China's Cultural Revolution, and it bought time for other Asian dominoes to shore up their defenses.

Not only was the war necessary, I argued, but it was winnable with better strategic decisions. The most momentous blunder was the decision of the American ambassador to South Vietnam, Henry Cabot Lodge, to foment the coup that overthrew Ngo Dinh Diem, which wrecked the South Vietnamese security apparatus and led North Vietnam to initiate a huge invasion of the South. Another mistake was Johnson's decision to not insert American ground forces into Laos to block the Ho Chi Minh Trail, a move that would have transformed the war and reduced the need for American forces.

 [...]

In the absence of presidential cheerleading, American public support for the war declined over the course of 1967. As administration officials had feared, the apparent weakening of American resolve hardened the determination of the North Vietnamese to persist. Hanoi rebuffed every American overture for peace negotiations, anticipating that the coming Tet offensive would destroy what remained of America's will.

In other words, the public's turn against the war was not inevitable; it was, rather, the result of a failure by policy makers to explain and persuade Americans to support it. Today, with the country engaged in two distinct, long-running conflicts and the possibility that others could flare up at any moment, it's a lesson that our current leaders should take to heart.