Behind the scenes, the relationship grew further strained. Al-Qaeda demanded regular reports on the disposition of the Islamic State’s fighters and offered pointed counsel on how to advance the State’s agenda. The Islamic State waved it away as mere advice, the distant frettings of men who had no clue about the rough realities of Iraqi insurgent politics.

The only times the Islamic State acceded to Al-Qaeda’s wishes was in regard to external operations. The Islamic State’s soldiers desperately wanted to take the fight to Iran and Saudi Arabia, which Al-Qaeda vetoed for one reason or another. The Islamic State grudgingly bent the knee.

When the Syrian revolution slid toward civil war in 2011, Al-Qaeda ordered the Islamic State to dispatch some of its operatives there to build a terror network. The Islamic State’s secret Syrian branch, called the Nusra Front, initially behaved like the Islamic State, carrying out attacks without a care for civilian casualties. But over time, Nusra began to follow the advice of Al-Qaeda’s leadership, which cautioned its members against killing Sunni civilians and counseled them to embed in the broader insurgency against the ruling regime. The strategy was at odds with the Islamic State’s plan of going it alone.

The incompatible strategies ultimately led to a rupture between the Islamic State and Nusra. After failing to quietly bring Nusra to heel, the Islamic State’s leader announced publicly that Nusra had been a secret branch of the Islamic State all along. Nusra’s leader responded by denying the Islamic State’s authority and pledging a direct oath of allegiance to Al-Qaeda’s leader, al-Zawahiri.