From Reuters:

U.S.-backed Syrian militias cut the last main road out of Islamic State-held Raqqa on Monday, severing the highway between the group’s de facto capital and its stronghold of Deir al-Zor province, a militia spokesman said.

The rapid collapse of the Islamic State’s territory is no accident.  It took months to build up steam in Iraq for the all-out assault on Mosul, always IS’s most important prize.  Once that assault was underway, the rest of the so-called caliphate could not hope to resist a concerted effort to destroy it.

In April 2015 I wrote about how the Islamic State was floating the idea of a truce – a decision that would have been wise if it had been serious.  But the caliphate’s ideology demanded greater and greater acts of purity and extremism – rather than moderating to survive, IS became more ruthless.  This ruthlessness worked in its favor in the chaos of the Syrian civil war and the withdrawal of U.S. troops in Iraq, but it was not a governable plan.

There is a lesson here: ideological purity of any stripe more often than not dooms nation-states to failure.  The Islamic State was not a nation, but it sought to use a hardline form of Islam as a means to build one out of the remnants of Syria and Iraq.   This might have worked had IS been left alone (though it could well have failed just as the Communist attempt to invent a Soviet also failed), but IS went out of its way to attack every state that might have ignored it – Turkey, Iran, France, Germany, and the United States.

Such geopolitical irrationalism did have some strategic sense to it: IS could only attract recruits so long as it appeared both strong and principled, and attacking these targets did both.  But the wide array of targets meant it was only a matter of time before a grand alliance formed to crush it.

That alliance – of Russian-backed Assadists pushing up from Palmyra, Turkish-backed Free Syrian Army units coming from the west, and U.S-backed Syrian Democratic Forces – will soon meet on the battlefield.  Will this be another meeting on the Elbe?  Will Syria be divided up, formally or informally, as Germany was?  We will know soon enough.