That many governments outside the US are skeptical about any US-led invasion of Iraq, when not openly opposed to it, is well known. Less recognized is the division between America and much of the world on how to combat terrorism. That division is dangerous.

It is not surprising that attitudes diverged so soon after the initial solidarity that followed the terrorist attacks on New York and Washington in September 2001. After all, the tragedy of September 11 ^th happened within the US, so the sense of immediacy was greater and longer lasting there. In Europe, many governments are anxious not to frighten their populations or damage relations with their Muslim minorities. Some believe that American foreign policy was partly responsible for the disaster and that it would be wise to distance themselves somewhat from the US.

Perhaps the most important factor opening this divide was a widespread sense of déjà vu. Europe lived through severe terrorist episodes in the 1970s and 1980s, yet managed to overcome them with their democracies intact. Terrorism (most Europeans think) is a nuisance to be managed, not a challenge requiring total change. Moreover, the political rhetoric of "evil" and "war" that mobilizes Americans seems alien to those who prefer a managerial approach.

Different perceptions are natural among different political cultures. Unchecked, however, these conflicting views could have dangerous effects by limiting the cooperation that is needed to address common vulnerabilities. Such cooperation is essential because today's terrorism is markedly more lethal and difficult to manage than earlier versions.

Two sets of trends are at work. The first centers around economics and technology. Market forces and openness combine to increase the efficiency of many vital systems--transportation, information, and energy--but also make them more vulnerable.

Democratization of technology enables instruments of mass destruction to become smaller, less costly, and more readily available. Where bombs and timers were once heavy and expensive, plastic explosives and digital timers are light and cheap. Hijacking a plane sometimes costs little more than the price of a ticket.

The information revolution has also helped terrorists, providing inexpensive means of communication and organization that allow groups once restricted to local and national police jurisdictions to become global. Thirty years ago, instantaneous global communication was mostly restricted to large entities (governments, multinational firms, the Catholic Church) with big budgets. The Internet makes it virtually free.

The second set of trends reflects changes in the motivation and organization of terrorist groups. Mid-20 ^th century terrorists tended to have relatively well-defined political objectives, which were often ill-served by mass destruction. Many were supported and covertly controlled by governments.

At the century's end, radical groups grew on the fringes of several religions. Most numerous were the tens of thousands of young Muslim men who went to fight against the Soviet occupation of Afghanistan. Terrorism became more brutal and indiscriminate as motivations changed from the limited and political to unlimited or retributive objectives reinforced by promises of rewards in the afterlife.

Organization also changed. Al Qaeda's network of tens of thousands of people in loosely affiliated cells in some sixty countries gives it a scale surpassing anything seen before.

Both trends make managing terrorism more difficult. Today's focus is properly on terrorism associated with Islamic extremists. But limiting attention to Islamic terrorists would be a mistake, because it ignores the wider effects of the democratization of technology and the broader set of challenges that must be met.

New technologies have put into the hands of deviant groups and individuals destructive powers once limited to governments. Every large group of humans contains members who deviate from the norm. Some are bent on destruction. Recall that a homegrown anti-government fanatic, Timothy McVeigh, perpetrated the worst case of terrorism in the US before September 11th, 2001. Similarly, the Aum Shinrykio cult that spread the poison gas sarin in Tokyo's subway in 1995 had no connection to Islam.

Indeed, whatever the source of terrorism, its lethality is increasing. In the 1970s, the Palestinian attack on Israeli athletes at the Munich Olympics or killings by the Red Brigades cost dozens of lives. In the l980s, Sikh extremists bombed an Air India flight, killing 325 people. Destroying New York's Twin Towers cost several thousand lives.

If one extrapolates from these trends and envisions some deviant group gaining access to biological or nuclear materials, it is possible to imagine terrorists murdering millions. To kill so many people, deviants like Hitler or Stalin needed a totalitarian government. But now it is easy to envisage deviant groups and/or individuals killing millions without state support. This "privatization of war" dramatically changes world politics.

The next step in the escalation of terrorism will have profound effects on the nature of our urban civilizations. What would happen to our willingness to live and work in cities, to real estate prices, to museums and theatres if instead of destroying two office buildings, a future attack destroys the lower half of Manhattan or the Left Bank in Paris?

Today's terrorism is nothing like the 1970s terrorism of the IRA, ETA, or the Red Brigades. Not one but many societies are vulnerable. One need not accept all the rhetoric or policies of George W. Bush to recognize that he is correct on a central point. Business as usual will not be enough.