Lesson two: Every war against jihadists fails to destroy anything except entire countries, as in Iraq, and wins the jihadists support. It is imperative to recognize a few things here: (1) the nation-state in this part of the world is a fragile institution; (2) anti-Western sentiment runs deep and wide across the Middle East; and (3) in consequence of (2), wars against jihadists draw ever-more people, most of whom are otherwise ordinary, to their cause.

The take-home: The greater the battlefield success of any Western coalition, the greater the overall failure.

The Islamic State’s strategists appear to know this stuff cold—which is why, as everyone admits, they are winning the propaganda war. This mob of savages traces its roots to the Sunni militias fighting the U.S. troops President Bush sent into Iraq in 2003. As they see it, Americans destroyed their country in front of their eyes and installed a Shiite government. Disaffected Sunnis, many of them alienated youths, saw appeal in ISIS, which rebased in Syria before returning southward.

Make no mistake about the brand. The cause is the redress of Sunni grievance, which is why Abu Bakr al-Baghdadi, a militant Islamist claiming Muhammad as an ancestor, was chosen to create and lead the Islamic State. But it is chock-a-block with orphaned officers from Saddam Hussein’s army—Ba’athists, who are nominally secularists and more than nominally spoiling for a fight against the Americans. This is why the ISIS armies have been so phenomenally successful on the battlefield.