Gian P. Gentile. New York Times, 31 October 2009.
http://www.nytimes.com/2009/10/31/opinion/31iht-edgentile.html?_r=1
Excerpt:
History shows that occupation by foreign armies with the intent of changing occupied societies does not work and ends up costing considerable blood and treasure.
The notion that if only an army gets a few more troops, with different and better generals, then within a few years it can defeat a multi-faceted insurgency set in the middle of civil war, is not supported by an honest reading of history.
Algeria, Vietnam and Iraq show this to be the case.
Defense Strategy Review 