After the conflict, he took time off to earn his PhD in international relations at Oxford University in England, where his research took him in a direction far from the military fashion of the time: COIN. His doctoral thesis focused on the successful British counterinsurgency campaign in Malaya (now Malaysia) against a communist uprising in the 1950s and the American experience in Vietnam. He argued that the key to Britain's success was to avoid civilian casualties as much as possible and have a robust strategy to win uncommitted local populations to the British side. In Vietnam, he concluded, the US relied on firepower and "kill ratios" to the detriment of winning over locals.
The book that emerged from his thesis, "Learning to Eat Soup with a Knife," was probably destined for good reviews, appreciation among specialists, and public obscurity. But when it was published in 2002, the US was confronting the trauma of Sept. 11. Two years later, as a largely Sunni Arab insurgency blossomed against US forces in Iraq (where Mr. Nagl was serving not far from Fallujah), many politicians and commanders came to believe that something different had to be done. Counterinsurgency doctrine beckoned, and Nagl was charged with helping to change the way the Army thinks about war.