How should one define the group that, under different names, has produced a genuine tragedy in parts of northwestern Iraq? Before the true extent of the group’s atrocities became widely known, devotees of the politically correct discourse referred to the group as “militants.” At the start of his presidency in the US, Barack Obama labeled the precursors of the group as “extremists.” He shied away from describing them as “terrorists” because that was the term that his predecessor George W. Bush had used. In Western Europe, those who still chase the mirage of multiculturalism suggested an even friendlier term: “Islamic fighter.”

So, is the self-appointed Caliph Ibrahim of the “Islamic State,” aka Abu Bakr Al-Baghdadi, an extremist, a militant a, terrorist or an Islamic fighter?

It may be possible to suggest that none of these terms accurately describe a movement that operates across quite different ideological trajectories. The terms used so far all imply the existence of a spectrum of behavior that can be understood in terms of human reality.

An extremist is someone who pursues an ideological objective with exceptional zeal by investing more than his share of time and energy in trying to achieve it. Extremists are found on both ends of the ideological spectrum, right and left. Mikhail Gorbachev was a mainstream Communist of his time while Kim Il-sung of North Korea was the extremist version. On the right, Iran’s Mullah Mohammad Khatami is the mainstream version of the same ideology of which Mullah Mohammed Omar in Afghanistan is the extremist. The trouble with the Islamic State of Iraq and Syria (ISIS) is that it has broken out of any conceivable range of political activity.

The term “militant” does not fit ISIS either. A man, or a woman, who spends more than a fair share of his or her time to promote an idea or a political program within acceptable rules of behavior, could be regarded as a militant. Such people exist in all political parties, trade unions and cultural associations. They are the ones who attend all meetings, going door-to-door to peddle their ideology, and spend their days off and holidays working for the cause. Their aim is to score points by working harder than others in the context of fair competition. That term does not apply to ISIS because it recognizes no rules apart from those set by itself, and does not want to win an argument through hard canvassing. It does not even want to impose any point of view, just its naked and brutal domination.

The term terrorist is also inapt in the case of ISIS. A terrorist tries to instill fear in an adversary from whom he demands certain concessions. For example, the Basque movement ETA used bomb attacks and individual assignation of officials as a means of forcing the government in Madrid to consider independence for the Basque provinces. However, ETA did not want Spain to obey its rules in every single aspect of life. ISIS, on the other hand, uses murder and mass murder as an end in itself. It does not want to persuade, cajole or convince anyone to do anything in particular; it wants everything.

The term “Islamic fighter” is equally misplaced for ISIS. An Islamic fighter is a Muslim who fights a hostile infidel who is trying to prevent Muslims from practicing their faith or, worse, entice them to apostasy. That, however, was not the situation in Mosul. No one was preventing the city’s Muslim majority from practicing their faith, let alone forcing them to convert to another religion. ISIS kills people because they simply exist as human beings. In any case, both in Syria and Iraq, ISIS has killed more Muslims than members of any other religious community. A Muslim fighting against the occupation of his land by a hostile power may also be regarded as an Islamic fighter, as is the case with some in Chechnya. Even there, indiscriminate killing as practiced by ISIS would have no place.

So, if none of the terms discussed above apply to ISIS, how can one define a phenomenon that has made even Al-Qaeda, the Taliban, Boko Haram and the Khomeinist gangs appear “moderate” in comparison?

The international community faced a similar question in the 18th century when pirates acted as a law unto themselves, ignoring even the most basic norms of human interaction. The conundrum was discussed in lengthy negotiations that led to the Treaty of Utrecht (1713) and the Treaty of Rastatt (1714). In order to define the lawless pirates, a new judicial concept was developed: crime against humanity. Individuals who committed that crime would be described as “enemies of mankind” or “hostis humani generis” in Latin. That meant that individuals and groups convicted of such a crime were no longer covered by any penal code or even the laws of war. They had set themselves outside humanity by behaving like wild beasts.

In the 18th century Britain used the concept to hunt down pirates across the globe, notably in the Caribbean. Thomas Jefferson, the third US President, invoked the same principle to justify sending an expedition to wipe out pirates in Algiers. After the Second World War, the Allies used the same concept to put Nazi chiefs on trial in Nuremberg. For the past 10 years, the United Nations has referred to the same concept in a series of trials against the Khmer Rouge mass-killers in Cambodia.

ISIS represents a marriage of nihilism and crimes against humanity. Like the pirates of yesteryear it has attracted criminals from many different nationalities. In fact, the European Union estimates that 2,000 of ISIS’s 10,000 fighters are citizens of EU states. There are also Tajiks, Uzbeks, Pakistanis and Russians from Dagestan. Because ISIS does not want anything specific, there can be no negotiations with it. Because it recognizes no laws, not even the laws of Islam, there is no reason why it should be treated with judicial kid gloves.

ISIS is not an Iraqi or Syrian or Lebanese problem, but a problem for the human family as a whole. It is not the enemy of any particular religion, sect or government: it is an enemy of humanity and deserves to be treated as such.