On September 11, 2001, David Levering Lewis was in Morocco, on the first leg of a research trip for God’s Crucible, a book intended to be a short history of the conflict between Islam and Christianity in eighth-century Europe. “My wife and I were in the casbah of Rabat when we heard of the attacks,” Lewis recalls, “and I said to her, 'this will be a rather different book—and a bigger book.’ ”

Now Norton is publishing God’s Crucible: Islam and the Making of Europe, 570—1215. As the subtitle indicates, God’s Crucible now sweeps across more than half a millennium. It still paints an admiring portrait of al-Andalus, as Muslim-ruled Spain was called: a polyglot society in which Arabs, Jews and Christians mingled comfortably and profited from a dynamic economy. But it also traces that civilization’s decline, in terms that make contemporary parallels only too evident. “Religious fanaticism became dominant, pushing out the pluralistic, sophisticated society that had existed for some 400 years.”

At 71, Lewis is trim and dapper, with the urbane, polished manner of a cosmopolitan intellectual. Born in Little Rock, Ark., his family were educated, high-achieving African-Americans, the kind of people famously dubbed “the Talented Tenth” by W.E.B. DuBois—subject of Lewis’s two-volume biography (W.E.B. DuBois: Biography of a Race, 1994; W.E.B. DuBois: The Fight for Equality and the American Century, Holt, 2000).

Lewis got his B.A. from Fisk University in 1956, his M.A. in American history from Columbia in 1958, and went on to get his Ph.D. at the London School of Economics. And while he says that he always felt there were no limits to what he might accomplish, in London he was “less conscious of being a person of color than I had been at Columbia.” London was wonderful for him, as was Africa, where he taught history at the University of Ghana in 1963—1964. His students came from villages; “they were smart and driven and a pleasure to teach.”

Lewis’s early academic appointments at American universities were all in French history, and he published a book about the Dreyfus affair, Prisoners of Honor (Morrow, 1973). But he also wrote King: A Critical Biography (Praeger, 1971), When Harlem Was in Vogue: The Politics of the Arts in the Twenties and Thirties (Knopf, 1981), The Race to Fashoda: European Colonialism and African Resistance in the Scramble for Africa (Weidenfeld & Nicholson, 1988) and, of course, the magisterial DuBois biography, which won him, among other prizes, two Pulitzers. He was awarded a MacArthur fellowship in 1999.

Lewis believes that it’s the obligation of those in the academy to reach out and compete with journalists to make what they know accessible. “We talk ceaselessly today about the global economy,” Lewis says. “Well, history must be global as well.”

God’s Crucible vividly illustrates Lewis’s point. In the eighth and ninth centuries, the West was bigoted and backward, the Islamic world tolerant and modern—but as Muslim Spain collapsed, its rulers turned to Islamic fundamentalism to bolster their power, while Christian Europe embraced the enlightened heritage of ancient Greece, sparked by Renaissance intellectuals’ rediscovery of classical texts that had been preserved by “the encyclopedic and rationalist Andalusian thinkers.”

Lewis thinks that his book’s themes of tolerance, of the dangers of fanaticism, are themes that we need to be alert to. It’s difficult for liberty to find purchase in cultures that are beleaguered and he believes that certain aspects of Western civilization should be universal: the sense of the individual as independent from the state and the rights of women are at the top of his list. But, he says, “When the United States presumptuously declares, 'These are the parameters for your development’ and lists everything else on a chart of evils, it harkens back to Innocent III and to Charlemagne saying to the Saxons, 'You will practice the kind of Christianity we want, or we will persecute you.’ ”

Lewis will leave in February for Berlin to take up a fellowship at the American Academy. He plans to incorporate a comparative study of Weimar Berlin and the Harlem Renaissance into the seminar he teaches at NYU on Europe and Africa. New York and Berlin in the 1920s and ’30s, he notes, were “two great cities where outsiders were trying to make a difference.” At the culmination of his distinguished career, Lewis certainly qualifies as an insider, although it’s clear he hasn’t forgotten what it feels like to be an outsider, and he continues to vigorously believe that history can, and should, make a difference.