KNOWING YOUR ALLIES:

A decade ago in Sadr City, a sprawling Shiite suburb of Baghdad, the Mehdi Army, led by Shiite cleric Moqtada al-Sadr, began to fight bitterly against American forces, calling them occupiers.

Now the Mehdi army has been re-branded the Peace Brigades, and it's fighting alongside Iraqi security forces against the Sunni extremists known as the Islamic State. American warplanes support their operations.

But even in Sadr City, not everyone's sure about militias playing such a big role. In a shop selling doves, canaries and birdseed, Abbas Naim expresses some doubts. He volunteered for the Peace Brigades after swaths of Iraq fell to the Islamic State earlier this year; right now he's on leave from duties in Samarra, north of Baghdad.

"Not everyone is as disciplined as the Peace Brigades," he says.

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