"In the last five years, the United States invaded two countries and overthrew two ruling parties. In Afghanistan and Iraq, the so-called 'end of major combat operations' came swiftly and decisively. In their wakes emerged resistances far more resolute than predicted, forcing coalition military commanders to shift from a conventional warfare doctrine to one better suited for fighting long wars against asymmetric enemies with extremist ideologies. But while religious extremism may typify the average insurgent, the biggest threat to American policy is not posed by the jihadist, who in most cases, lacks the ability to organize, effectively train and recruit forces (other than suicide bombers), and has no long-term strategy for generating resources, garnering public support, or achieving realistic strategic goals. The real hazard to American objectives in Southwest Asia comes from armed and active militias who, unlike most insurgents, have served as career soldiers, seized the support of their populace, and, in many cases, infiltrated national government institutions."
Parameters, US Army War College Quarterly: http://http://carlisle-www.army.mil/usawc/Parameters/