Al-Qaida in Iraq emerged after al-Zarqawi pledged his allegiance to Osama bin Laden, leader of the global al-Qaida network, in October 2004.
A revolt against al-Qaida by Sunni Arab tribes in western Iraq in late 2006 and 2007 deprived the group of its main bases of support. Taking advantage of the vulnerability, the U.S. pummeled the group during the 2007 troop buildup.
Although al-Qaida has shown it is still capable of carrying out its hallmark coordinated suicide attacks against high-profile targets in the heart of the capital, all indications are the organization has been significantly degraded since the height of the insurgency, said Brett McGurk, a fellow at the Council on Foreign Relations and former U.S. National Security Council and State Department official. Estimates put its highest strength at one point at close to 10,000 fighters, mostly Iraqis, but the number is thought to be much smaller now.
The spate of violence after al-Zarqawi was killed "was basically al-Qaida saying 'you can kill our top guy but we're still around and we're still in control of events,' " McGurk said.
He said the current situation is much different because al-Qaida is weaker and Iraqi security forces are stronger, but that the true test will be in the coming months: "Can al-Qaida pull off spectacular bombings and if they can, how do Iraqis respond?"