The Defense Department "tends to just assume that it's good — it's part and parcel of the strategy of assembling as big a coalition as possible, but I'm not sure that's the right way to think about it," said Stephen Biddle, adjunct senior fellow for defense policy at the Council on Foreign Relations. "A major U.S. interest in this conflict is to prevent the war from spreading and sucking in the neighbors and destabilizing more countries than just Syria and Iraq. And one good way to destabilize more countries is to get them drawn into larger and larger military involvement in this conflict."
"There are lots of people in Jordan who are sympathetic to [Islamic State]," Mr. Biddle said. "There are others who hate them. You could easily imagine, especially once ISIL decides it has a military reason to engage in terrorist activity in Jordan, that this war could become very divisive in Jordan over time. And the last thing we need is another — much less several more — countries with civil wars going on and in which there's a risk of state failure and government collapse."