By Barbara F. Walter

Over the weekend, everyone has been asking the same question: why would ISIS bomb Paris? Or a Russian airliner for that matter? Or Beirut or Ankara? Why draw the ire of powerful countries like France, Russia, Lebanon, and Turkey when the most likely result is a doubling down of their attacks against the group? Isn’t this self-defeating?

In short, the answer is no, it’s not. ISIS is pursuing a very clear strategy and it just might work. In a study of terrorist strategies, Andrew Kydd and I lay out five ways that groups like ISIS achieve their objectives. We term one of these methods a war of attrition strategy. It works in two ways. First, a war of attrition communicates to the target that the terrorist group is not only willing – but also able – to kill their citizens and that it will continue to do so until the target stops attacking them. Second, it communicates that the terrorist group is willing to absorb more pain and hold out longer than the target. The implicit message is this: as long as you continue to fight us, we will strike back and you will give up sooner than we will.

ISIS’s terrorist attacks are part of a war of attrition strategy. Currently, the biggest threat to ISIS comes from outside states. The United States, Australia, the UK, Canada, Holland, France, Jordan, Turkey, Russia, and Egypt have all engaged in air strikes against ISIS. Iran, Hezbollah, and Russia have all sent troops to fight ISIS directly. Their increasing attacks have been a game-changer. Until each of these countries increased their involvement this summer, ISIS was doing quite well; the group had captured almost all Sunni territory in Iraq and was dominating other rebel groups in Syria. Since the airstrikes began, however, ISIS has lost significant territory and is on the defensive.

The terrorist attacks are designed to change this. ISIS is hoping that countries like France will cut-and-run in the face of brutal attacks. But why would countries do this? The answer has to do with domestic politics. The victims of terrorist attacks are often average citizens who have a voice in who governs their country. The greater the number of terrorist attacks that affect these citizens, the more pressure they will put on their governments to stop the violence, and the more they will question the war against ISIS.

The logic of ISIS’s strategy, therefore, doesn’t seem so silly and self-defeating after all. It’s forcing powerful countries – many of them democracies with voters who are not convinced that Syria and Iraq are worth fighting for – to choose between greater security at home for their citizens or greater involvement in ISIS’s wars. There’s a real trade-off to be made and the choice is not clear, especially if the terrorist attacks begin to add up.

The Friday attacks on Paris will almost certainly convince France and the vast array of outside states arrayed against ISIS to increase their attacks. But when this happens, leaders in Paris, Washington, London, and Moscow should understand that this will also increase ISIS’s incentives to launch more terrorist attacks against their citizens, not fewer. Yes, security can be beefed up. But even the most sophisticated anti-terrorism strategy cannot prevent all attacks from getting through. So the question to ask ourselves is this: are we willing to trade the possibility of an ISIS-free Middle East for more terrorist attacks in Paris, New York, Chicago, London, Hamburg, Moscow, Ottawa, and Rome?