How did ISIS come to be defined as a terrorist group? A sociologist explains:

While there are a number of militant groups in Syria that foreign governments could focus on, ISIS has three things that makes it appear as a pressing threat. First, ISIS’s sudden advances in Iraq were an unanticipated event, and consequently created a media spectacle. No one really expected the Iraqi central government or Kurdish authorities to lose control of major cities and sites so quickly. Once they did, there was a major story there. Second, and related, the group has territorial control. While ISIS had controlled territory in Syria and Iraq previously, the declaration of an Islamic State in late June creates a clear target. There is little evidence that the Islamic State intends to directly attack outside of Iraq and Syria, but territorial control signals capability and threat, in the same way that aviation attacks do, as Miner and I argued in our study. Finally, ISIS engages in classically “terrorist” behavior—beheadings of captives and attacks on civilian populations. In essence, it’s the combination of sudden success, territorial control, and markers of terrorism that bring attention to the Islamic State.

None of these are sufficient explanations by themselves…

Even before the video-taped beheadings, the attacks on Yezidis and other religious minorities seemed to signify international terrorism to the American public. There’s a seemingly odd confusion here in public opinion. While the Taliban in Afghanistan never carried out international terrorism, they were the target of the American response to September 11th just as much as Al-Qaeda was. Similarly, in Iraq, various militant groups were seen as international terrorists even without action beyond the context of the Iraqi Insurgency. Americans have thus learned to think of any militant Islamic group as terrorists; all the group needs to do is reveal its Islamicness. Attacks on religious minorities certainly do that. In this environment, beheading hostages is just another marker, especially as it echoes the acts of previously militants defined as terrorists—Al Qaeda’s beheading of Daniel Pearl in 2002 or the frequent beheadings of captives by Al Qaeda in Iraq during the Insurgency…

ISIS really demonstrates the large amount of variation there is among “terrorist” groups. There are lots of different ideologies, lots of different goals, and lots of different types of groups among militants. While policymakers and the public tend to view certain forms, such as transnational networks of Islamists, as threatening, organizational forms might be best seen as different ways of solving resource dilemmas and meeting goals.

Appears to be a combination of militant Islam and specific actions like drawing attention through victories, controlling territory, and beheadings. But, it still has to be defined as terrorism – these traits on their own don’t automatically confer such a status unless other states and actors do so. When it is the United States or other powerful bodies doing the deciding, a matter of definitions can matter quite a bit.

One implication here is that switching up a few things such as changing the specific place (the Middle East already draws extra attention given recent years) or the religious background of the group or actions receiving less media attention might lead to a very different definition of the group.