http://www.worldaffairsjournal.org/2009+-+Summer/full-Marlowe.html
(this is a very long article, please see the link for complete text)
At the time of the U.S. invasion of Iraq in March 2003, counterinsurgency theory was about as popular in American military circles as tank warfare is today. An early study by the chief war planner for the 101st Airborne Division during its first deployment to Iraq reported “a collective cognitive dissonance on the part of the U.S. Army to recognize a war of rebellion, a people’s war, even when they were fighting it.” There was a reason for this. Eager to forget the most painful experience in its history, the army had all but banished counterinsurgency from the lexicon of American military affairs after Vietnam. As a result, the army relied on a flawed strategy in Iraq for a period that lasted, according to author Thomas Ricks, at least “twenty months or more.”
As U.S. Army Colonel Gian Gentile has summarized this line of argument, there was a “bad war” in Iraq fought by officers who ignored the theory and practice of counterinsurgency, followed by a “good war” fought by its champions. In Vietnam, however, even the “bad” war was fought by commanders deeply versed in the tactics, techniques, and procedures of counterinsurgency (COIN)—much more, in any case, than their counterparts were on September 11, 2001. The United States may have gone, in James Fallows’s memorable phrase, “Blind into Baghdad.” It did not march blindly into Vietnam. On the contrary, counterinsurgency theory enjoyed a special vogue in the 1960s: it was certainly more fashionable and better understood by an educated public than it is today. Especially among military officers, COIN was more roundly known during this era than at any time up until the release of Field Manual 3-24 in December 2006.
A May 1964 article in Harper’s magazine, “Books on Guerrilla Warfare—Fifteen Years Overdue,” mocks what it presumes to be a shallow and fleeting interest in COIN among the power elite. “Already we are suffering an over-production of doctrine,” Eric Larrabee laments, even though doctrine is “relatively useless without the fine-grain detail.” He places David Galula’s now canonical Counterinsurgency Warfare in the category of “High Policy,” and counterinsurgency experts Charles T. R. Bohannan and Napoleon D. Valeriano in the “For the Professional” group. Larrabee reserved the “Recommended” designation for the highly specialized 1956 volume Guerrilla Communism in Malaya, by Lucian Pye, a prolific Sinologist and advisor to President Kennedy. He mentions in passing Viet Minh General Võ Nguyên Giap’s People’s War, People’s Army, along with an anthology of Marine Corps Gazette articles, The Guerrilla and How to Fight Him.
There were very good reasons for this popular interest. The great success of Mao Zedong in China and the proliferation of Communist guerrilla warfare were deemed to be second only to the Soviet nuclear arsenal as threats to America’s national security. Counterinsurgency theory emerged in response to Mao’s doctrines of revolutionary warfare, and it was studied in the postwar period with an urgency that still has no corollary today. That the accumulation of all this knowledge generated so few results in Vietnam—certainly fewer than it has generated lately—is one of the great puzzles of American military history.