In the new issue of the American Prospect, available online now (but subscribe!), I have a long review of Fred Kaplan's book The Insurgents

Short version: this is a good and important book that you should read.

Medium version: see the review itself.

Full version: check out the book.

Here is a sample of the argument:
Kaplan describes how the COIN [counter-insurgency] approach eventually "succeeded" in Iraq, by which he means that it bought enough stability to allow American forces to withdraw in something other than outright retreat. In Afghanistan it has failed even that modest test; indeed, Kaplan argues, the comparative successes in Iraq lured the U.S military, especially [Gen. Stanley] McChrystal, into attempting the impossible in Afghanistan. The government in Kabul was even more corrupt and less legitimate than the one in Baghdad; Afghanistan had a far weaker tradition of centralized control of any sort than what Saddam Hussein, for better and worse, had brought to Iraq. Kaplan summarizes Australian strategist David Kilcullen on the paradox that doomed U.S. efforts in Afghanistan:
Reduced to a syllogism, his argument went like this: we shouldn't engage in counterinsurgency unless the government we're helping is effective and legitimate; a government that needs foreign help to fight an insurgency generally isn't effective or legitimate; therefore, we generally shouldn't engage in counterinsurgency.
It was a return, 40 years later, to one of the main lessons of Vietnam. By the end of America's war there, our military had gotten much better at a kind of war that it realized it was better off choosing not to fight.
Explaining ideas through biography is so attractive an approach as often to seem this era's cliché in magazine and book writing. Of course, authors from the time of Herodotus onward have understood the explanatory power of biography, but I date its modern popularity and occasional overuse to the influence of David Halberstam's The Best and the Brightest and Robert Caro's The Power Broker, both in the early 1970s, followed by Neil Sheehan's A Bright Shining Lie in the 1980s.

The Insurgents stands out as a particularly effective and legitimate use of this approach, and one whose clarity and drama should extend its audience far beyond the normal defense-policy crowd.