This brings us back to Friday’s events. ISIS advanced last week in part because Russia supported a fierce Assad ground offensive against U.S.-backed anti-ISIS rebels. Many anti-ISIS rebel groups hold positions both in the center of the country, where the offensive took place, and on the front lines against ISIS in the north. One group was even bombed by both ISIS and Russia on the same day near the rebel-ISIS front lines. While U.S.-backed rebel groups normally rush north to repel ISIS offensives, this time, the fierce Russian assault in the center of the country kept them pinned down.

A second reason ISIS is gaining is that Russian jets interfere with the anti-ISIS coalition. Coalition air raids, despite their serious flaws, have at times beaten ISIS back. But with Russian jets flying in Syrian airspace, U.S. planes are diverting their routes to avoid conflict. Last week, the Pentagon reported two such diversions between Turkey’s Incirlik Airbase and the ISIS stronghold of Raqqah. That flight path runs directly over the towns ISIS just conquered. We can surmise that this is making it easier for ISIS to operate, and we can only imagine how much ISIS would have gained if U.S. forces had left Syrian airspace, as Putin abruptly demanded last month.

While the U.S. and Europe want to beat ISIS, Putin’s main goal is to co-opt the anti-ISIS fight.