It used to be rational, rather. The classic terrorists of the &#x27;70s wanted &quot;a lot of people talking but not a lot of people dead&quot; -- and also wanted to survive the experience. The new breed of terrorism in the &#x27;80s and &#x27;90s was different from those; the IRA, the PLO, and various state-sponsored terrorists in that period had&#x2F;have more in common with each other, despite their obvious differences, than any have with al-Qaida and ISIS, which aim for suicide missions with high body counts.<p>This particular operation is either ISIS-conducted or ISIS-oriented vigilanteism; whichever it is, backing down in Syria will only embolden them. (Or rather, embolden those like them; I don&#x27;t imagine that very many of the specific attackers here are going to have particularly many opportunities to do this again in the future.)<p>ISIS is specifically out for either world empire or apocalyptic defeat (see <a href="http:&#x2F;&#x2F;www.theatlantic.com&#x2F;magazine&#x2F;archive&#x2F;2015&#x2F;03&#x2F;what-isis-really-wants&#x2F;384980&#x2F;" rel="nofollow">http:&#x2F;&#x2F;www.theatlantic.com&#x2F;magazine&#x2F;archive&#x2F;2015&#x2F;03&#x2F;what-isi...</a> ); tactical concessions will work about as well as they did with the Nazis and the Communists -- or even less well than that, since neither Naziism nor Communism believed that success was a sign that Divine Providence was smiling on them.