Background to the Surge
Kimberly Kagan, who taught history at West Point, gathers the disparate "open source" (i.e. news stories) to describe the battle for Baghdad leading up to the Surge and suggesting what lies beyond.
The United States does not have enough forces in Iraq to defeat the insurgency through raids and strikes. These types of military operations cannot eliminate the entire network of terrorists or weapons caches faster than they regenerate. ... Eliminating large weapons caches and known insurgent strongholds in the Baghdad beltway helped set the conditions for the Baghdad Security Plan to unfold more safely. But it is difficult to see any path by which targeted raids and strikes would end the insurgency without an area security plan.
I hope to add more comments after reading this long and very worthwhile article more carefully. But just on first impressions, the narrative shows the battle on the ground does have a shape. The sheer scale of the engagements, the size of caches and the intensity of the enemy effort is a clear indication that the US is not fighting ghosts, but a highly organized and well-funded enemy force. Far from being an effort which Iran and al-Qaeda can engage in effortlessly, the intensity of the action and the resources involved imply that it is taking its toll of them too, not only in materiel but in creating enmities which will take a long time to resolve.
However, as matters stand, the regional enemies may be able to feed the fight better than the US. They may lose every engagement, but their ability to generate forces even in the face of heavy casualties gives them hope they will retain possession of the battlefield by sheer persistence. On the face of it, the "area security plan" Kagan refers to can only be provided by an Iraqi Army. The military rationale for building an Iraqi state is therefore ultimately a requirement for warm bodies on a scale that the US could never and will probably never be able to provide.