ISHAQI, Iraq — Fearful of a future as violent as the past, and exasperated by corrupt and incompetent politicians, the men who hold power here have seized the moment of American departure and national political chaos to administer their own form of justice: expelling suspected insurgents and their families from this town with the threat of death.

Where they go, the sheiks do not care.

“Anywhere, but not Ishaqi,” said Sheik Hussein Saydoon, a tribal leader in this Sunni-dominated backwater just off the highway between Baghdad and Tikrit, Saddam Hussein’s hometown. “If they came back, they would be killed immediately. This is what it’s all about.”

Here and in other towns, in the interplay among tribal chiefs, elected officials and security forces, a new Iraq is taking shape. It may be buttressed by new ideas of democracy, but it is still very much dominated by the centuries-old customs and swagger of tribal leaders, quick to welcome outsiders with offers of sweet chai and platters of kebab and chicken but capable of swift acts of justice that can supersede those of any court.

Many of these sheiks once led teams of Awakening fighters, former Sunni militants whose decision to switch sides and fight alongside the Americans altered the course of the war and demonstrated the supremacy of tribes in effecting change in rural corners of Iraq. They said that the departure of the American military and the ensuing political crisis in Baghdad, which raised fears of a return to sectarian warfare, prompted them to take matters into their own hands.