Ilich Ramirez Sánchez, the Venezuelan radical with the nom de guerre Carlos, has recently been back in the news for the first time in a long while. He has been imprisoned in France since being captured in Sudan seventeen years ago. Now the French are trying him again for some more of his crimes—in this case a series of bombings in the early 1980s. Carlos, represented in court by a female lawyer he married in prison several years ago, looks and sounds as smarmy and unrepentant as ever.

Carlos's eclectic terrorist career got him involved with partners as varied as the Popular Front for the Liberation of Palestine, East Germany and Iraq. He also has traversed a lot of ideological ground. He inherited his Marxism from his father, who showed his political leanings with the names he chose for his children: Ilich's brothers were named Vladimir and Lenin. But while in prison Ilich/Carlos converted to Islam and wrote a book titled Revolutionary Islam in which he expressed support for Osama bin Laden. An odd transition if you think about the substance of the ideologies—godless Marxists are intellectually far, far away from the radical Islamism that bin Laden purveyed.

A common mistake in trying to understand what makes Carlos—or any other radical individual, group or regime—tick is to try to draw too much out of the ostensible substance of whatever ideology they are spouting or subscribing to at the moment. Radical ideologies do serve important purposes for radical actors, but the purposes are mostly served by having any such ideology, not by the tenets of a particular ideology. We err in declaring things like World War IV and viewing radical Islam as fundamentally different from militant challenges of the past because of purported afterlives or any other ostensible elements of an official system of beliefs.

For Carlos or most any other terrorist leader, either radical Marxism or radical Islam or radical something else will serve as the rationale for a career of violence. Some radical ideologies will serve better than others only for reasons having to do with what happens to have resonance or currency in the time or place the terrorist is operating. At his current trial Carlos identified himself as a “professional revolutionary”—an apt description and one not dependent on his being a Marxist or an Islamist or anything else. (Another example in international terrorism that has exhibited an ideological blend of Marxism and Islamism is the Iranian group Mujahedin-e Khalq.)

For individuals who get swept up in terrorist groups, Marxism or Islamism or something else serves as what the late Israeli scholar Ehud Sprinzak called an “ideological master-key”: a coherent belief system to reassure him that he has done the right thing by forsaking other attachments and getting into the dangerous and difficult business of terrorism. Again, the specific content is less important than having some such belief system. And the belief system is less important than personal circumstances and grievances in propelling the individual into that business in the first place.

For regimes and states, radical and non-radical alike, ideologies serve still other purposes (including for our own state, although we usually do not like to apply the term ideology to the belief systems that undergird our own political culture). As for states subscribing to a revolutionary ideology such as Marxism-Leninism, the experience with the likes of the USSR and China tells us that although ideology does leave an imprint, it is less influential than the basic state and regime interests of power and survival. The same is true of a revolutionary, or ostensibly revolutionary, Islamist regime such as Iran.