On September 5, German police raided a house near the village of Oberschledorn, about an hour's drive east of Düsseldorf, and arrested three suspected Islamist terrorists. They had accumulated enough hydrogen peroxide to build a bomb with the explosive power of 550 kilograms (1,200 pounds) of TNT, and they had scouted potential targets like Frankfurt Airport and the huge U.S. air force base at Ramstein. As usual, the German police released only the suspects' first names and initials: Daniel S., age 22; Fritz G., 28; and Adem Y., 29.

It was the closest call yet for Germany, which has so far escaped attacks like those in Spain and England. More attempts will doubtless follow, for Germany has peacekeeping troops in Afghanistan and Lebanon, and the disaster in Iraq has poisoned the well so badly that western troops in any Muslim country look like part of the "Zionist-Crusader assault on Islam" to some young Muslims. But the response of the German media was instructive.

There was, inevitably, the "blame the immigrants" gang, like Jacques Schuster in the Berliner Morgenpost: "The government must increase the pressure on Muslims to integrate. Even peaceful parallel societies cannot be tolerated." This kind of missed the point that two of the three men arrested were ethnic German converts to Islam. (The other was a Turkish citizen long resident in Germany.)

There was also the realism and refusal to panic of a society that has some previous experience dealing with terrorism, in the days of the Baader-Meinhof Gang. As Stephan Speicher put it in the Berliner Zeitung: "We will just have to learn to live with the threat of terror. At some point, people will die. It is surprising, therefore, how calmly society is reacting, even though everyone must realize that the security agencies cannot be successful forever."

But the most trenchant comment came from Richard Meng in the Frankfurter Rundschau: "It was Fritz and Daniel who were arrested with Adem, not Mohammed or Mustafa. It can no longer be denied that it is foolish to regard immigrants as a greater security threat than the indigenous population. It is even more foolish to make sweeping judgments about Islam." Exactly.

"Islamist" extremism is a political phenomenon, and it has precisely the same appeal to the disoriented and the alienated as previous millennial doctrines, from the Hashishin (Assassins) of the 12th-century Middle East to the anarchists and Bolsheviks of 20th-century Europe. Like many such doctrines, it wraps itself in religious symbolism: most religions are, after all, millennial. But terrorism is not religion, and "Islamism" is not Islam.

First- and second-generation immigrants from Muslim countries who have not found their feet in western countries are prime recruits for "Islamist" doctrines, of course, but so are alienated people in the host society, like Fritz G. and Daniel S. in Germany or the Jamaican-born, British-raised London bomber Abdullah Shaheed Jamal (born Germaine Maurice Lindsay). Those people thought they were converting to Islam, but they were actually attracted by the violent, apocalyptic fervour of the extremists. Emotionally, all forms of political extremism are virtually interchangeable.

So what lessons can we draw from this? First, the potential terrorists are already in the West, and all the border controls in the world will not stop them. At least 90 percent of the terrorist attacks in western countries come from people who live in those countries, not outsiders trying to get in.

True, a lot of them go to camps in the more lawless parts of Pakistan for "training", but this is something that should be warmly encouraged. The training is obviously not very good, for few of the bombs have worked and few of the terrorists have even gotten to the point where they have actually tried to blow something up. And it was travelling to Pakistan that first put them on the watch lists of western security forces: all of those "terrorist training camps" are obviously infiltrated by people who hand over lists of the foreign visitors to western controllers.

This is a 20- or 30-year game of spooks and terrorists that will play out mostly on the margins. Border controls are of minor importance in the game, and invading foreign countries is almost invariably counterproductive.

Every incident will be represented by some government official as "al-Qaeda–linked", as if there were some criminal mastermind planning all these attacks. True to form, Germany's interior minister, Wolfgang Schäuble, announced that the three current suspects, and 10 others who are being sought, "obviously planned these attacks on the orders of an international network". But it's really scattered local stuff that follows an ideological and tactical template that is now available everywhere on the planet.

Osama bin Laden created the template, so in that very limited sense, every "Islamist" attack has an al-Qaeda link, but the organization itself is no longer a major player. The sporadic terrorist attacks in western countries will continue, but they will be far less destructive than those in Muslim countries and they will certainly diminish if western troops pull out of Muslim countries. So the German approach is just right: do the intelligence work, don't overestimate the threat, and, above all, don't panic.