Five years after the war in Iraq began, the insurgency remains a lethal force. The steady flow of cash is one reason, even as the American troop buildup and the recruitment of former insurgents to American-backed militias have helped push the number of attacks down to 2005 levels.

In fact, money, far more than jihadist ideology, is a crucial motivation for a majority of Sunni insurgents, according to American officers in some Sunni provinces and other military officials in Iraq who have reviewed detainee surveys and other intelligence on the insurgency.

Although many American military officials and politicians -- and even the Iraqi public -- use the term Al Qaeda as a synonym for the insurgency, some American and Iraqi experts say they believe that the number of committed religious ideologues remains small. They say that insurgent groups raise and spend money autonomously for the most part, with little centralized coordination or direction.

Money from swindles in Iraq and from foreign patrons in places like Saudi Arabia allows a disparate, decentralized collection of insurgent cells to hire recruits and pay for large-scale attacks...

...A military official familiar with studies on the insurgency estimated that half of the insurgency's money came from outside Iraq, mainly from people in Saudi Arabia, a flow that does not appear to have decreased in recent years...

Paying former insurgents to stop attacking American forces and join neighborhood militia forces has played a crucial role in turning around security in many Sunni parts of Iraq. But American officers worry that the failure to incorporate these Sunni militiamen into the government of Iraq or find them other jobs could portend trouble.

"There's got to be an outlet," the senior military official said, referring to a job and salary not related to the insurgency. "Without that outlet, a lot of guys will gravitate back. They are not going to starve their families. You have got to do what you have got to do to survive."