BAGHDAD — The two men knocked on Abu Salam's door on a Friday morning. He was one of the last remaining Christians on his block.
"Peace be upon you," they said, and Abu Salam, a man in his 50s, repeated the greeting.
The pair, one fat and the other thin, spoke politely. Both were cleanshaven and wore slacks and button-down shirts.
"You are now aware the neighborhood of Muwallamin belongs to the Islamic State of Iraq," the bigger man said. "We have three conditions you can accept: You can pay a tax, become a Muslim or you can leave your house and we will help you take out your furniture.
"We'll let you make up your mind.
"Peace be upon you," the men repeated as Abu Salam watched them leave.
Within hours, Abu Salam and his family left their neighborhood of more than 50 years. They joined an exodus that has all but emptied Dora, a large district in south Baghdad, of its once-thriving Christian population.
Abu Salam, who spoke on condition that he not be fully identified, citing fears for his safety, is staying elsewhere in Baghdad for now.
"People will leave if things don't get better. It is chaos," he said. "If there is no imminent solution, Iraq is finished."
Christian leaders say 500 families left Dora in April and May. The U.S. military acknowledges that a large number of Christians were uprooted but says the number is significantly less. The United Nations' refugee agency said it counted 100 families at one location who had fled Dora.
The flight of Dora's Christians is an example of how the initial phase of the U.S. security crackdown here has failed to establish security and stop the sectarian "cleansing" of Baghdad's neighborhoods.
The U.S. military conducted a major clearing operation in Dora last fall, then largely pulled out, turning security over to Iraqi forces. Sunni Arab militants with ties to the group Al Qaeda in Iraq quickly reestablished themselves and late last year began harassing Christians. A second U.S. sweep in early winter failed to loosen the militants' grip on Dora.
Displaced Christians described in interviews a civilian population too terrified of Al Qaeda to ask Americans for help. They said that even after the Baghdad troop buildup started in February, U.S. soldiers were rarely present in some neighborhoods and often had no idea what to look for.
Maj. Kirk Luedeke, the U.S. military spokesman for Dora, said U.S. officials were caught off guard by the campaign against the area's Christians. "We knew it was going on; we just didn't know how widespread it was," he said.
Iraq's senior Christian politician, Younadam Kanna, said the military didn't launch an offensive against militants in Dora until May 25, though the campaign to drive out the district's Christians had begun in earnest in late April.
"There weren't enough forces," Kanna said. "The multinational forces are isolated from the people.... They don't know who is who. The MNF and even the government had poor information in that region."
In response to the mass displacements, the U.S. military has strengthened its presence in the area. In a bid to contain Al Qaeda supporters and prevent further neighborhood purges, the U.S. Army has erected concrete barriers and walled off certain streets.
Troops are surveying every home, collecting photographs, fingerprints and retinal scans of all military-age males to monitor the population in case of another bout of sectarian cleansing. With the additional troops, the U.S. Army says it can patrol every neighborhood in Dora, sometimes several times a day.
The Christian community's troubles in Dora can be traced to autumn 2004, when Sunni militants bombed churches and kidnapped people. But Christians' lives irrevocably changed for the worse after Al Qaeda and allied groups declared an Islamic State of Iraq in October.
By January, the Islamic State's proclamations appeared on walls and were circulated in leaflets. Dora residents said some of the fliers called on women to wear veils; shorts and cellphones prohibited.
"They issued laws and decrees like a real state," said Wardiya Yussef, who left in April after a cousin was shot on the street.
Bodies were dumped regularly on the main street of her neighborhood. Papers demanding protection money were sent to homes.
As Al Qaeda backers flexed their muscle, Iraqis were reluctant to give information to the Americans. It was a bitter reversal from the period last fall when military sweeps in Dora had briefly restored stability. In that regard, too, Dora fits a broader pattern in which civilians have watched U.S. troops come and go, seldom staying long enough to establish lasting security.
That lack of constancy has bedeviled U.S. efforts in Iraq, said Stephen Biddle, a military analyst at the Council on Foreign Relations.
"Until local civilians come to believe that you'll be there long enough to protect them from reprisals -- and that you're stronger than the militants while both are present -- they won't trust you well enough to risk offering tips and information."