I think the problem is that the enemy changed the rules and the generals unlike the foot soldiers took a lot of time to understand it (if they even have). http://www.theatlantic.com/magazine/archive/2012/11/general-...

There are no military objectives or territory worth holding for them. Their goal is to just inflict as much pain as possible on the US troops knowing that they can outlast them. The US has army that can deal with any conventional threat (from which there are few) or properly defined objective, but seems unprepared for country occupation/building mission (and with good reason, the Army as a foreign policy tool is not wise).