The Iraqi extremist group didn't conquer a major chunk of the country on their own. They had help - from ex-Saddamites, tribal councils, and other militants. "Non-ISIS groups played a central role in the takeover," Hassan said.
Tactical details from the past week's offensive are hard to come by. But Hassan says the groups that cooperated with ISIS include: "The Sufi-Baathist militia known as the Army of the Men of the Naqshbandi Order, which has former members of the Iraqi army during Saddam Hussein's reign. The Al Qaeda-originated Ansar al-Islam, and provisional tribal councils, many of the which are actually front groups for the Naqshbandis," according to Hassan.
War can be a centrifugal force, pulling together disparate groups who share a common enemy. It's after the heat of battle when it comes time to divvy up the spoils and work out power sharing arrangements, that yesterday's allies turn on each other.
"That's where jihadi groups have always failed in the past," said Fishman. "ISIS has built a military coalition," he said "at this point they haven't fully demonstrated it can be a governing coalition. If this crumbles in the near term it won't be because Baghdad gets it act together but from the coalition coming apart."
Whether ISIS can maintain the partnerships that allowed it to get this far is uncertain. What is certain, a grim and unavoidable reality at this point, is that Iraq is once again at war, and has a ruthless fundamentalist power lodged in the heart of the country.
So how many sleeper cells are waiting Baghdad for ISIL to issue the go order?