Instead, Mr. Breivik’s goal is to reverse what he views as the Islamization of Western Europe; indeed, he sees himself as a soldier in a defensive war against “Islamic imperialism.” In his view, Muslims are colonizing Europe, helped by high birth rates and a doctrine of multiculturalism advocated by the European elite. Islam, for him, represents an existential threat to European civilization, a threat that must be countered at all costs. The best way to do so, he argues, is to wage war against “cultural Marxists” — his label for the European political and intellectual elite — because they are the traitors who allow the colonization to take place.

While Mr. Breivik’s violent acts are exceptional, his anti-Islamic views are not. Much, though not all, of Mr. Breivik’s manifesto is inspired by a relatively new right-wing intellectual current often referred to as counterjihad. The movement’s roots go back to the 1980s, but it gained substantial momentum only after 9/11. Its main home is the Internet, where blogs like Jihad Watch, Atlas Shrugs and Gates of Vienna publish essays by writers like Robert Spencer, Pamela Geller, Bat Ye’or and Fjordman, the pseudonym for a Norwegian blogger. Mr. Breivik’s manifesto is replete with citations of counterjihad writers, strongly suggesting that he was inspired by them.

Of course, by advocating the mass murder of European politicians, Mr. Breivik goes much further than any counterjihad ideologue has ever done, and his manifesto contains ideas and information that have no precedent in the counterjihad literature. For example, he provides extensive advice on how to build bombs and plan terrorist attacks. The leading counterjihad writers have virtually never advocated violence, and several of them have condemned Mr. Breivik’s actions.

He also claims to be a member of a knightly order called the European Military Order and Criminal Tribunal, which he describes as a reincarnation of the Knights Templar and which he says he founded in London in 2002 with activists from eight countries across Europe.

Indeed, the more belligerent part of Mr. Breivik’s ideology has less in common with counterjihad than with its archenemy, Al Qaeda. Both Mr. Breivik and Al Qaeda see themselves as engaged in a civilizational war between Islam and the West that extends back to the Crusades. Both fight on behalf of transnational entities: the “ummah” — or “community” of all Muslims — in the case of Al Qaeda, and Europe in the case of Mr. Breivik. Both frame their struggle as defensive wars of survival. Both hate their respective governments for collaborating with the outside enemy. Both use the language of martyrdom (Mr. Breivik calls his attack a “martyrdom operation”). Both call themselves knights, and espouse medieval ideals of chivalry. Both lament the erosion of patriarchy and the emancipation of women.