From Foreign Affairs:
ISIS is not al Qaeda. It is not an outgrowth or a part of the older radical Islamist organization, nor does it represent the next phase in its evolution. Although al Qaeda remains dangerous—especially its affiliates in North Africa and Yemen—ISIS is its successor. ISIS represents the post–al Qaeda jihadist threat…If ISIS is purely and simply anything, it is a pseudo-state led by a conventional army. And that is why the counterterrorism and counterinsurgency strategies that greatly diminished the threat from al Qaeda will not work against ISIS.