France must take measures to protect its citizens, as must the United States, Russia and all the other countries — Western and Middle Eastern — threatened by the Islamic State’s murderous dream of a new caliphate. At the same time, it’s clear that the prevention of further ISIS attacks will require threatened states to find a way to end the Syrian civil war, which has made it possible for this terrorist group to gain wealth, territory and power. That means closely coordinating action among countries already engaged in the fight — most notably the United States and Russia — and it means persuading more European and Middle Eastern nations to join in the mission.