Thirty minutes of terror on the streets of Paris looks to become the catalyst for a broad shift in international politics with implications that could last for years. Much of the focus in the West over the past year has been on a perceived growing threat from Russia. Terrorism was a real, but containable problem. Moscow’s new aggressive military posture in Ukraine and beyond, on the other hand, posed a more serious threat. But with a series of well-coordinated strikes, Islamic State put the threat of terrorism back at the center of the international agenda. And Russia, far from a nuclear-armed enemy, instantly presented itself as a partner—one with a plan for immediately tamping down the threat.