“Oh, East is East, and West is West, and never the twain shall meet, / Till Earth and Sky stand presently at God’s great Judgment Seat.” Anthony Pagden doesn’t quote Kipling’s famous lines in “Worlds at War” (Random House, 625 pages, $35), his colorful and informative book about the dire things that have happened when the twain have met over the last 2,500 years. It would be surprising if Mr. Pagden, a historian at UCLA, did quote Kipling, at least unironically. The poet’s frank imperialism, his earnest belief in the irreconcilability of races and civilizations, has long been taboo in intellectual circles. As long ago as 1942, George Orwell wrote that “it is no use pretending that Kipling’s view of life, as a whole, can be accepted or even forgiven by any civilized person.”

Yet the subtitle of Mr. Pagden’s book — “The 2,500-Year Struggle Between East and West” — shows how, in the post-September 11, 2001, era, this once-discredited worldview is roaring back to life, under the more neutral name of “the clash of civilizations.” With Osama bin Laden and his accomplices vowing to restore the seventh-century caliphate, it is once more possible to think of civilizations as having essences, which do not change, rather than potentialities, which do. This covert essentialism is what makes “Worlds at War,” for all its righteous passion in defense of the West and its freedoms, a troubling book. In his eagerness to point out what is admirable in the Western tradition — liberty, individualism, reason, the separation of religion from power — Mr. Pagden risks turning history into a Manichean pageant, in which the West is always fighting for justice against an unjust and unreasonable East.

This is an old-fashioned way of viewing history, and Mr. Pagden often sounds like a Whig historian, chronicling the triumph of progress over its stubborn enemies. His method is to retell some of the most famous chapters in European history, from ancient Greece to World War I, in each case focusing on the conflict between a variously defined Europe and a variously defined Asia. These events come down to us heavily encrusted with myth: From the Persian Wars to the Crusades to Lawrence of Arabia, they are stories Europe has used to explain itself to itself. Ordinarily, one would expect a historian to approach such myths with forensic caution — to probe for the facts beneath the legends, and above all to complicate what time has simplistically moralized.

Yet Mr. Pagden’s approach is just the opposite. He seems to want to revive the power of these myths in order to restore ideological confidence to an apathetic Western public. “It seems unlikely that the long struggle between East and West is going to end very soon,” he writes on the book’s last page. “The battle lines drawn during the Persian Wars more than twenty-three centuries ago are still, in the selfsame corner of the world, very much where they were then.” It is the kind of call to arms we might expect from a politician or a polemicist. Coming from a historian, it is surprising, because it seems to negate the first principles of history, which are contingency and change. If Americans are Athenians and Muslims are Persians, then nothing that has happened since the Battle of Marathon really matters; history is not a process, still less a progress, but an eternal deadlock.

The odd thing is that Mr. Pagden’s book, simply because it traverses so much time and space, effectively undermines its own thesis. Take the Persian Wars, the first act in the clash of civilizations, in which a grand Eastern despotism, ruled by the Achaemenid monarchs Darius and Xerxes, tried to snuff out the small but resilient democracy of Athens. It is certainly true that, had the Greeks lost the battles of Marathon and Salamis, the course of European history would have been different. Mr. Pagden quotes J.S. Mill’s verdict that Marathon was “a more important event in English history” than the Battle of Hastings, when the Normans conquered England itself.

Yet the closer one looks at this history, the more ambiguous it becomes. Athens may have been a democracy in the early fifth century B.C.E., but it had not been one a hundred years before, and it wouldn’t be one a hundred years later. The foundational works of Greek political thought, Plato’s “Republic” and Aristotle’s “Politics,” were antidemocratic in tendency. On the other hand, the culture of the Ionian Greek cities that were under Persian rule was hardly stifled by Eastern despotism: The origins of philosophy lay with Ionian Greeks like Heraclitus and Anaximander. All this suggests that, had Persia extended its overlordship to the west coast of the Aegean, much that we prize in Greek culture would still have existed, though in different form. Certainly the fate of democracy as a political system could not have been permanently decided by just two battles.

If even today we remember Persia as an effeminate despotism, the first incarnation of an eternally menacing East, it is largely because of the way this image was perpetuated by later writers. It is thanks to Herodotus, Mr. Pagden shows, that the Persian Wars became a morality play about the superiority of Greek isonomia, or equality before the law, to Persian absolutism. Yet conveniently, two centuries later on, when Alexander the Great reversed Xerxes’s campaign — leading a Greek empire on an aggressive campaign into Asia — the stigma of despotism did not attach to him. On the contrary, as Mr. Pagden writes, what looked like monolithic imperialism in the Persians was, in Alexander, an enlightened vision of a world state: “[H]e introduced into Greece, and subsequently into the whole of Europe, an ambition for universalism that would determine the future of the continent.” According to one 20th century historian Mr. Pagden quotes, the League of Nations itself could be traced back to Alexander’s example.

This sort of rewriting of the past in line with the concerns of the present is not exactly blameworthy. It is how the past is made to live; perhaps we can only be perfectly objective about histories we no longer care about. Yet it also blurs the complex truth of history and encourages us to draw a too straight line between past and present. Everything we currently prize about our civilization is made to flash out at us from each moment of our past, while everything that currently shames us is tactfully draped.

Nor is it only the West that engages in this sort of mythologizing. We can see it at work, for instance, when the Ottoman emperor, Mehmed the Great, the conqueror of Constantinople, visited the site of Troy in 1462 and declared: “It was the Greeks … who ravaged this place in the past, and whose descendants have now through my efforts paid the right penalty, after a long period of years, for their injustice to us Asiatics at that time and so often in subsequent times.” Of course, there was no connection at all — ethnic, religious, or linguistic — between the Turks and the Trojans, and not much more between the Byzantines and the Achaeans.

By insisting that European and Asian were transcendental, eternal identities, Mehmed was simply harnessing the emotions of the past to the policies of the present — just as Virgil did when he claimed that the Trojan prince Aeneas had founded Rome. Or, more to the point, as Ayman al-Zawahiri did when, just after September 11, 2001, he compared the attacks to the Battle of Hattin, where Saladin defeated the Crusaders in 1187. In his closing pages, Mr. Pagden makes clear that today it is Islamic fanatics, dreaming of ancient power and purity, who are most enamored of the myth of an eternal hostility between East and West.

Yet Mr. Pagden’s response, it often seems, is to reciprocate that hostility: to identify Islamic fanaticism with Persian absolutism, and to dismiss both as representatives of an eternally malignant Asian or Eastern identity. This leads him to some startlingly simplistic and moralistic judgments. “History in the Islamic world … has always moved at a different pace,” he writes; or again, “Islam is a simple faith, which is certainly one reason for its success.” It is hard to imagine that any scholar of Islam or the Middle East — which Mr. Pagden is not — would ever write this way about a faith and a civilization that span continents and millennia.

Inevitably, such antagonism to the East leads to an unearned complacency about the West and its values. In “Worlds at War,” the essence of the West is always found in Pericles and Montesquieu, never in Nero or Napoleon. A more balanced approach would acknowledge that, if the West has achieved things we hold sacred — as we should — it has always been the result of internal struggle. What are now the cherished principles of Western civilization, from democracy to racial equality, have all started out as critiques and became generally accepted only after long and sometimes violent conflict. For much of the world, much of the time, the most conspicuous qualities of the West were its violence, intolerance, and lust for domination. The African slave trade and the Holocaust, too, belong to the historical identity of the West. “Worlds at War” would be a more convincing book if it took account of the fact that wars over principles and values don’t just take place between worlds, but within them.

akirsch@nysun.com