In its global reach and in its aggressive intentions, Islamist ideology bears some resemblance to another transnational belief system: namely, Communism. Like today’s Islamists, Communists of an earlier age saw themselves as engaged in an apocalyptic struggle in which every member of a Communist party anywhere was expected to comport himself as a frontline soldier, and in which terror was seen as a wholly permissible means toward victory in a war to the finish. Compare Stalin’s “If the enemy does not surrender he must be exterminated” with the refusal of the leader of Hizballah in Lebanon to negotiate with or ask concessions from the West because “We seek to exterminate you.” To Sheik Omar Bakri Muhammad, a Syrian with British citizenship who until recently led a group called al-Muhajiroun, the terrorists of September 11 were “The Magnificent Nineteen”—or, as he explains, the advance guard of an army of “our Muslim brothers from abroad [who] will come one day and conquer here.”

Throughout the cold-war era, the European democracies under threat from Soviet expansionism were themselves home to Communist parties, as well as to an array of front organizations ostensibly devoted to peace and friendship and culture but in reality manipulated by and for Soviet purposes. In addition, many people from all walks of life accommodated themselves to Communism with varying degrees of emotional intensity and out of various motives, including the wish to be on what they perceived as the winning side and the converse fear of winding up on the losing side.

Each of these elements, in suitably transmuted form, is present today. The pool of local recruits upon which Islamists draw is itself very large. Of Europe’s 20 million Muslims, it is estimated that 5 or 6 million live in France alone, at least 3 million in Germany and 2 million in Britain, 1 million apiece in Holland and Italy, and a half-million apiece in Spain and Austria.