"APPEASEMENT!" What a powerful term it has become... It is much stronger a form of opprobrium than even the loaded 'L' word," writes Paul Kennedy, the distinguished assessor of empires at Yale and a Commander of the Order of the British Empire, in his provocatively titled "Time to Appease," in The National Interest.

He acknowledges that it's "risky to ask," even "in a scholarly way, whether acts of appeasing a rival might not sometimes be a good thing. You wanted to continue negotiations with Saddam Hussein? Appeaser.... To wriggle out of Afghanistan? Appeaser. . . Before such abuse of the term gets worse, perhaps we should all take a small History lesson."

Actually, Kennedy's "small history lesson" is magisterial in its specificity and range, but indeed it's as risky as his purpose in offering it: to commend appeasement, not only in rare circumstances, but as a more general policy, to would-be grand strategists (including one at Yale) who've hurled the "A" word at policymakers they consider insufficiently vigilant and aggressive. This controversy is more than semantic. Is there a way out?

Kennedy knows what it's like to be on the receiving end of this kind of "A"-bomb. He condemns statesmen who accommodated rising fascism in the 1920s and 30s, but he insists that "This great [American] hegemon, like all who have preceded it..., cannot escape the constraints of history and geography. Its culture, ideology and domestic politics mean that it can never become Alexandrian, Roman or Napoleonic....

He cites the Princeton political scientist Aaron Friedberg's "rather wonderful book entitled The Weary Titan.... about how a worried Great Britain began to come to terms with the changing world order around 1900,... but it really was a subtle plea for Washington to make a cold-blooded assessment of how many overseas commitments it could sustain over the long haul."

That is Kennedy's plea now, too, and, ever since he published The Rise and Fall of Great Powers in 1987, he's been called a "declininst" who reads the British Empire's descent onto America's future.

The neo-conservative historian Robert Kagan's Dangerous Nation, a bellicose celebration of an expansionist America, is a virtual rebuttal to Kennedy. And it was Kagan's father, Donald Kagan, a scholar of Thucydides and a colleague of Kennedy's at Yale, who actually hurled the "A" word at him in 2001.

A week after the attacks of September 11, the elder Kagan published a column in the Yale Daily News assailing Kennedy and Strobe Talbott -- the former Clinton under-secretary of state who in 2001 was directing Yale's Center for the Study of Globalization (he now heads the Brookings Institution, where Robert Kagan is now a fellow) -- for reckoning not with the threat of terrorism posed by the attacks but, he charged, with "reasons that caused the perpetrators to act and our need to understand and sympathize with them."

Donald Kagan's column -- re-published immediately by the neo-conservative Weekly Standard -- reminded its readers that intellectuals of the 1930s had accepted Hitler's rise as a consequence of Weimar Germany's humiliation by World War I's victors.

Then Kagan wrote: "Kennedy's comments....seem to suggest we react by appeasing the terrorists by a measured retreat....

Noting that Kennedy, on a panel discussing the September 11 attacks two days after they'd occurred, had said that the United States "doth bestride the world like a colossus," Kagan retorted that when Shakespeare's Cassius said that about Julius Caesar, "he hated him and would soon plot to assassinate him" and that his words "probably reflect the feelings of the terrorists toward the United States and, apparently, those of Kennedy."

Such a breach of collegial decorum between eminent professors, especially in a student newspaper, is all-but unthinkable at Yale, where faculty communication is often conducted with arched eyebrows and significant silences. But Kagan had reason to feel aggrieved. In 2000 he and his other son Fred, a West Point professor and future champion of "the surge" in Iraq, had published While America Sleeps, its title an echo of their hero Winston Churchill's While England Slept.

"In the past," they wrote, "the collapse of an international system.... deprived Americans of access to markets or caused American casualties on faraway battlefields. In the future, it will bring attacks on the American homeland.... This warning, in many respects, is already too late.... Now the United States must begin to gird itself for the next round of conflict."

Liberals responded that, just as a stopped clock is right twice a day, obsessives like the Kagans do sometimes mark dangers that others miss but that they seem to live for those dangerous moments: For them, it's always 1938, when Churchill could only wring his hands over Neville Chamberlain's credulity about Hitler, but it's never 1914, when war fever spurred nationalists very much like the Kagans to cheer on the Götterdämmerung that would seed Hitler's rise.

The attacks of September 11 did seem to confirm the Kagans' darkest warnings and strategic doctrines, and, three days later, both Donald and Robert Kagan and their Yale colleague Charles Hill signed a public letter to President George W. Bush, written by William Kristol for the neoconservative Project for The New American Century, urging that "even if evidence does not link Iraq directly to the attack...the eradication of terrorism... must include a determined effort to remove Saddam Hussein."

History hasn't taken long to judge the wisdom of that presumption and the strategy behind it, but September 11 gave the Kagans a "teachable moment," as Bush and Britain's Tony Blair seemed to incarnate an injunction leaping right out of the West's great epics and chronicles: Sometimes, humanist Truth-seekers and republican Power wielders must fight together against common enemies. The attackers had been willing to die for their convoluted convictions and rage; were we willing to die for anything worth defending against them?

Kennedy acknowledges that, "Yes, there comes a time when you have to stand and fight; to draw a line in the sand." But he notes that the anti-appeasement crowd seldom rues Britain's 19th-century appeasements of the United States with territorial and other concessions, and they don't belabor American eagerness in the 1920s to keep up business dealings with Hitler's Reich and float loans for Mussolini. "When," he asks, "do you say to yourself, 'This guy can only be stopped by the threat of serious armed force and, most probably, having to use that force?'"

I'm not wholly on board with Kennedy here. Britain's "appeasement" of former colonists who were rising within a Western Enlightenment dispensation made a lot more sense than Chamberlain's truckling to fascists. And liberal democracy itself may have more at stake in a degree of continued American "hegemony," albeit one less swashbuckling and corrupt, than it would in anything that seems likely to replace it. Kennedy's benign omniscience about such matters is a relief from neoconservative bombast, but it sounds a bit weary, too. Since I posed this assessment yesterday in The Guardian, perhaps we'll learn what some of its British readers are thinking of such arguments now.

There's an alternative that neither Kennedy nor the Kagans address: Since 1947, powerful, armed regimes - of the British in India, segregationists in the American South, Afrikaners in South Africa, and the Soviets in Eastern Europe -- have been brought down without carnage thanks to shifts in popular beliefs about power and legitimacy that have shaken up the ancient relationships of power, violence, and viable authority.

As the classical historian Daniel Tompkins of Temple University puts it, "The field of international relations over the past two decades has witnessed a widespread discursive turn as many political scientists have noticed situations in which argument prevailed over force and state identity and ideation had causal functions."

With a depth and breadth worthy of Kennedy, the writer Jonathan Schell has traced the unprecedented emergence of such constructive, bottom-up configurations of power in whole societies, not fringe movements. His The Unconquerable World, published in 2004 and excerpted in Harper's at that time, shows why power resides at least a little less often now with those who give orders coercively than it does with those who either obey or disobey them creatively with enough good faith, courage, and discipline to avoid descending into the anarchy which the Kagans think always awaits them.

Schell's argument and the recent history driving it deserve far more consideration, and if the Kennedy-Kagan controversy continues, this author of one of this new century's neglected great books and, like them, a teacher at Yale, ought to be up on stage with them.