From Jeffrey White at the Washington Institute for Near East Policy:

An Adaptive Insurgency: Confronting Adversary Networks in Iraq
...What makes the networks in Iraq such a difficult target? At the core of the difficulty in dealing with the insurgency lies the fundamental nature of the insurgent networks themselves—social organizations, or organisms, more or less well adapted to the social environment, or “landscape,” of Iraq, especially Sunni Arab Iraq. The adaptive nature of these networks has made them resilient, capable of accommodating substantial military and political changes in the environment, and able to
survive. This paper broadly suggests what will work and not work in combating the insurgents. It makes the argument that only by changing the environment, or “landscape,” in which the insurgents operate beyond their capability to adapt to the change, can the insurgency be controlled. This approach goes beyond “oil spot,” and “clear, hold, build,” although those strategies do aim at changing aspects of the insurgents’ operational environment. It is closer to “winning hearts and minds.” But the adaptive capacity of the insurgents may surpass the ability of even this approach...