It began in the town of Hawija, near Kirkuk, where Iraqi Security Forces said Sunni protesters were harboring insurgents who had killed soldiers at a government checkpoint. The protesters denied there were any insurgents in their camp and failed to turn over any individuals. On April 23, the security forces launched an action in the camp — and a violent clash ensued, leaving scores dead and injured. Now Sunni Arab sheikhs who had been urging restraint are calling for war. Some reports say that the tribes are gathering former insurgents and preparing to fight. Violent incidents have already taken place, with more than 40 people killed in one day in Mosul alone.

This has the gravest implications for Iraq’s security and stability. Al-Qaeda in Iraq has already begun to reestablish itself in areas that Iraqi and U.S. forces cleared at enormous cost over the past five years. And Jabhat al-Nusra, al-Qaeda in Iraq’s front group in Syria, is attempting to hijack the secular resistance to Syrian President Bashar al­Assad. These developments threaten not only to unravel the gains made since 2007, but also to energize the forces of violent extremism in the heart of the Arab world, already burning in Syria. …

It is also incumbent on the friends of Iraq to support this effort. Progress in Iraq came when coalition elements encouraged Sunni communities to work with a government in which they still lacked trust. It is vital that the spirit that animated the progress then be reinvigorated now.