But it appears that an extra catalyst is the behavior of the government itself.
Hundreds of Iraqis are being tortured to death or summarily executed every month in Baghdad alone by death squads working from the Ministry of the Interior, the United Nations' outgoing human rights chief in Iraq has revealed.
John Pace, who left Baghdad two weeks ago, told The Independent on Sunday that up to three-quarters of the corpses stacked in the city's mortuary show evidence of gunshot wounds to the head or injuries caused by drill-bits or burning cigarettes. Much of the killing, he said, was carried out by Shia Muslim groups under the control of the Ministry of the Interior.
One point that should startle those who get their news from US outlets is just how long this has been going on.
He said figures show that last July the morgue alone received 1,100 bodies, about 900 of which bore evidence of torture or summary execution.
The US media has only paid slight attention to this aspect of the civil war in Iraq, and only in the last couple of weeks. This is important, since as long as the civil war was seen as being a one sided affair, with just the most radical of the Sunni involved, there is a reasonable expectation that moderates will put their faith in the government. When it becomes clear that aspects of the government are involved in trying to kill you, your family, your friends, you are far less likely to remain supportive of the government.
So while political and religious leaders call for calm, it is the people who have to accept this call. As long as the government is operating or allowing death squads to operate, there is little chance that the Sunni population will turn their back on the Sunni insurgents. As long as the Shia militias continue to exist, as long as the Ministry of the Interior continues to run death squads, torture centers and use summary execution as a tool of policing, the average Sunni will not turn their back on their radical insurgents.
As long as these dynamics remain in place we will have a civil war in Iraq.