The confrontation, presented by the corporate media as a struggle against Al Qaeda terrorists, has deep roots in the sectarian divisions that were instigated by the US war and occupation as part of a deliberate divide-and-rule strategy. They succeeded in pitting Iraq’s majority Shi’ite population against the minority Sunnis, while the Kurdish minority in the north has been allowed to pursue regional autonomy, while conflicts over borders and rights to oil wealth threaten to erupt into civil war there as well.For more information of the Empire's use of the "divide-and-rule strategy" see this, this, and this.
For their application of terror to destabilize Iraq see this.