LONDON--In the midst of anger and grief, here's the good news:

The London terrorist attacks were markedly less sophisticated than the 9/11 attacks on New York, the 3/11 attacks on Madrid and the 1998 embassy attacks in East Africa. The subway system the terrorists attacked is much less closely guarded than the airlines penetrated by the 9/11 terrorists. The timers they used are a technological notch below the cell phone detonators of Madrid. They were constrained to use less explosive--and fewer operatives--than in East Africa.

Nor did they use suicide bombers. That is an interesting and suggestive absence. In London, where subway riders are alert to unattended packages, a timed bomb would have to be quite small to escape detection--which may explain why the casualties inflicted by four explosions in confined spaces were relatively low. Suicide bombers could have carried much deadlier devices onto the bus or subway--or driven a car laden with explosives into London's centre.

So why did the planners of the London attack not make use of this technique? It's not a surprise that the planners declined to give their own lives--it's a notorious fact that the leaders of al-Qaeda, Hamas and other Islamic terror groups take care to preserve themselves. But were the planners unable to recruit British Muslims willing to blow themselves up? Or were they unwilling to trust British Muslims to carry a suicide mission through? If so, what prevented them from smuggling foreign terrorists into Britain?

We won't know for some time the answers to those questions. But pending better information, we can say that based on what we do know, the London bombings look like the work of an international terrorist network that is losing its effectiveness, its cohesion and some of its ideological attractiveness to radical Muslims in the West and worldwide.

Tougher laws, swifter action and better information are steadily degrading terrorist capabilities. And where is this information flowing from? In very large part from the Muslim communities of the United Kingdom and the West. Of necessity, this is a largely unreported story, and the individuals involved are glimpsed only in flashes--such as "a Muslim woman born in Britain who has voiced strong concern about radical clerics' influence on young immigrants there," who was briefly mentioned in a June 17 New York Times story as leading an investigation into Islamic extremist discussion groups.

Organized Islamic groups in the West have often played a troublingly ambivalent role in the war on terror. But the sheer number of arrests and plot interceptions achieved by U.S., U.K., and European security services--and the rarity of successful terrorist attacks--do seem to indicate that individual Western Muslims are acting on their own to police their own communities.

The terrorists too seem to have noticed this. I wonder if it was purely a coincidence that one of the July 7 bombs was detonated at the Edgware Road tube station--Edgware Road being the central thoroughfare of London Islam.

The U.K. police are indicating that they suspect the killers were Algerian. If true, this too is suggestive. Algeria was wracked by a fearful civil war in the mid-1990s, as Islamic extremists attempted to seize power and create a Taliban-style state in North Africa. More than 100,000 Algerians were killed, many of them in indiscriminate massacres of whole villages by Islamicist bands. Algerian Islamicists have learned to see their less fanatical fellow-Muslims as their main enemy--and moderate Muslims in Algeria have learned that there can be no religious solidarity with killers who dream of creating a religious totalitarian state. This is a lesson that has to be absorbed by Muslims worldwide.

This is the war now being fought all over the world, from London, England, to London, Ont. We are all in it, like it or not. And while good police work like that of the U.K. security services can minimize the harm this war does to the populations of the West, the war won't end so long as the totalitarian impulse within Islam rages on. In Algeria, the totalitarian impulse was subdued by superior force, but it was not discredited.

Two years ago, my writing partner Richard Perle and I warned in An End To Evil that while the war on terror can be lost in the cities of the West, it can never be won there. Totalitarianism is a powerful idea, and ideas can be uprooted from the minds of human beings only by more compelling ideas--of which the most compelling is the idea of democracy. That is the idea for which Britain and its coalition partners are now battling in Iraq. And that is why this latest, terrible attack must fortify the resolution of Western powers to do more than police their cities against each new round of murderers--it must spur us all to do what it takes to win.

David Frum is a resident fellow at AEI.