In the early 15th century, European nations began building overseas empires. At its peak, the imperial sway of the European powers was vast. David Abernathy, in The Dynamics of Global Dominance, European Overseas Empires, 1415-1980, estimates that "three-fifths of the world's population live in countries whose entire territory has at one time been claimed by a European state." In 1913, the homelands of European imperial powers took up about 1.6 percent of the earth's surface. They controlled another 41.3 percent overseas. Europeans once controlled the territory of two out of every three of the current members of the United Nations. In about a third of these cases, European rule lasted 250 years; in another half, it lasted a century or so. Only a handful of places—e.g., Japan, Thailand, Afghanistan, and what is now Ethiopia—did not have at least part of their territory controlled by Europeans.

Abernathy argues that the nations of Europe brought to bear on the world three sources of power: their public institutions (government and military); their private business establishments; and their religious organizations. Correspondingly, in the places that fell under their power, they altered political, economic, and spiritual life. Exerting this power did not produce versions of Europe overseas, except in usually superficial ways. It did, however, change fundamentally what had existed before. European power was able to establish and maintain itself and produce such powerful effects because it consisted of these three separate sources that combined with and supported one another in various ways.

Before launching on the imperial enterprise, these sources of power had been increased and tested in the process of competitive nation building that gave rise to a set of European nation-states. This process continued throughout the life of imperialism, motivating and strengthening it. Behind all these developments and driving them forward was a revolution in man's relation to nature, the appearance in Europe of modern science.

In the decades following World War II, formal European political control over imperial territories came to an end. Yet economic power remained, as did spiritual and political influence. The attacks of September 11 targeted symbols of two of the three sources of power that constituted Western imperialism: the economic and the political. (Interestingly, the religiously inspired attackers did not attack a symbol of European religion.) Because the recent attacks target not merely Western power but also the principles out of which it grew, as well as the civilian populations of the former imperial powers, the assaults mark a new stage in what might be called the imperial struggle.

The preceding stage, the European withdrawal from empire, did not occur because of a military challenge by indigenous peoples. Excluded from political institutions, they could not easily organize military forces; and even if they could, the disparities in power had become too great. The battle for independence, therefore, had to be political. The contradiction between respect for European principles (for example, majority rule) in Europe and the attenuation of these principles in the overseas empires afforded a fertile source of complaint. The inhabitants of British North America in the 18th century were the first to use this tactic with their rallying cry of "no taxation without representation." As this example indicates, the decisive struggle was fought among the indigenous peoples themselves. To quote John Adams, the American Revolution "was effected before the war commenced. The Revolution was in the minds and hearts of the people." This struggle for hearts and minds—this "people's war," as it came to be called in the 20th century—sought to negate European power, especially military power, not by confronting it directly but by making it irrelevant. The Europeans could win every battle but still lose the war because military victory could not lead to effective political control.

Violence had a place in the anti-colonial struggle. Those opposed to European control used violence, i.e. terrorism, to display their power, thus attracting the undecided to their cause, and intimidating both the locals who did not support independence and the Europeans who lived in their midst. Once intimidated and organized, the indigenous people became the basis of larger and more organized uses of force, what came to be called guerilla warfare. In a few instances (e.g., the North American colonies against Britain, North Vietnam against the French) indigenous forces attained a proficiency that approached what the imperial power could deploy. Generally, however, the anti-colonial forces were not capable of engaging European forces directly. Moreover, they were rarely and only in special circumstances (Irish violence in Great Britain; Algerian violence in France) capable of projecting violence into the imperial homeland, and even then took this step only when opposition to independence was unusually strong.

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Western imperialism and the forces that made it possible transformed the world. In fact, they made it possible to speak truly of world politics and a worldwide economic system. But those forces are now beyond the power of the West to control. We often hear about "blowback," the unfortunate consequences of our support for the guerilla fighters who resisted the Soviet invasion of Afghanistan. Callous as it may sound, if the September 11 attacks were part of the price that had to be paid for putting an end to the Soviet Union, it was still a bargain. But this price may pale in comparison to the potential blowback from European imperialism and the spirit that animated it. Western economic and scientific ideas and practices, so essential to globalization, have placed enormous power—financial, microbial, chemical, and nuclear—within the grasp of some and the reach of others who do not share, indeed who hate, the Western spirit.

The attacks on September 11 are the clearest indication yet that we are engaged in the next stage of the imperial struggle. Unlike the previous stage, the anti-colonial struggle, our enemies do not use our principles to undermine our confidence. They do not tell us that they seek to establish, even superficially, Western regimes, whether socialist or liberal-democratic. Instead, they seek a return to a pre-modern, non-Western, largely imagined world of Islamic purity.

To make room for this way of life and to preserve it, so they believe, they must fundamentally alter the balance of power in the world. Since their goal is so uncongenial to us, persuading us to support them will be harder, perhaps impossible. Thus intimidation with violence will be more important in this stage of the imperial struggle than in the previous stage. But as in the previous stage, our enemies will avoid direct military confrontation with us. They are yet incapable of that.

Instead, they pursue a strategy of people's war. Like their predecessors, they use violence against the West to display their power and recruit supporters. If our enemies gain more adherents and intimidate the governments of more Muslim countries, their power will grow. Perhaps some day they may be able to confront our military forces directly, should it come to that. Until then, they pursue people's war with a new twist—not only a political war for the support of indigenous peoples but a war waged directly against the imperial power's home population.

The strategy of direct attack on a civilian population is not unprecedented, of course, even within the West. It was a feature of European wars in both the 17th and 20th centuries, for example. As these cases suggest, such attacks perhaps should be expected in wars fought for principle, whether religious or political. But the European or Western liberalism that spread around the world did tend gradually to distinguish between civilians and professional soldiers, and afford the former a degree of protection from the terrors of war. In the United States, this liberal view contrasted with an older republican view that, to be fully a citizen, a man should be willing to bear arms and die defending his country. In a sense, the next stage of the imperial struggle has returned us, involuntarily, to this older understanding, though without its provisional protections for women and children.

As President Bush acknowledged, more American civilians than professional soldiers are likely to die in the war on terrorism. Without fully realizing it, perhaps, every American has been given by our enemies the awful privilege of facing death for his country's sake.