Just the facts first:
Iran, Iraq’s Shiite neighbor not only regards the Sunni derived Al Qaeda as a bitter enemy, but provided military assistance to the United States in Afghanistan to defeat Al Qaeda.
Iran is holding hundreds of Al Qaeda members in prison, and has been executing them.
Like the Shiite in Iran, the Shiite in Iraq consider Al Qaeda a bitter enemy and have been killing them as often as possible.
Many Sunni have already fled Iraq.
The conflict in Iraq, is a civil war.
Iran IS a Democracy, having political parties and elections.
Christians and Jews are free to practice their religion in Iran.
Christians and Jews are NOT free to practice their religion Saudi Arabia.
Those are the facts, here comes some common sense, intermingled with some probable facts:
Yes, there WILL be bloodshed. Decades of Sunni oppression, torture, and murder of the 80 percent majority Shiite in Iraq is going to result in payback, no doubt about it. But the fact is, that payback has already been underway since the US occupation began. Since no one with a grip on reality believes a military victory by the United States which ends the civil war is possible, the only possible conclusions as to what the United States is actually capable of accomplishing in Iraq are the following:
(a) A SLIGHT mitigation of the violence in very limited areas of the country, but with increases in other areas which pop-up as the fighters simply move.