The historian Fritz Stern once mused with Henry Kissinger about what would have become of them — both German Jewish refugees from Nazism — if Hitler had never lived. Mr. Kissinger speculated that he would have become a high school teacher; Mr. Stern, that he would have been a physician in his hometown of Breslau, like his father, both grandfathers, and all four great-grandfathers before him. What happened to Mr. Kissinger instead, the world knows; what became of Mr. Stern is the subject of his stately new memoir, “Five Germanys I Have Known” (Farrar, Straus & Giroux, 546 pages, $30).

For most historians, writing the story of their own lives is superfluous. Beyond their hours in the archives and the classroom, everything they have to say is in the pages of their books. Mr. Stern is a special case, both because of the dramatic disjunctions of his life and his unusually public and engaged career. Born in 1926, in the Silesian city that is now Polish Wroclaw, he was part of the generation of German Jews whose talents were denied to their homeland by Nazi anti-Semitism. Yet as the title of Mr. Stern’s memoir makes clear, much of his career as a scholar, writer, and adviser to governments has been spent finding a way back to his native country. Mostly scanting the personal, he tells his story in conjunction with that of the country he fled, studied, and pondered over. The five Germanys in question — Weimar, Nazi, West, East, and reunified — provided the intellectual and moral background to a life based in New York City, where Mr. Stern was for decades an eminent professor at Columbia University.

Nazi racism forced the non-Aryan Stern family out of Germany, even though they were not Jewish by faith. Fritz’s parents, Rudolf and Kathe, had both been baptized at birth, and the future historian grew up celebrating Easter and Christmas. Like much of the German Jewish bourgeoisie, however, the Sterns’ real religion was culture, Bildung, and especially science, Wissenschaft. On both sides of his family tree, young Fritz was related to eminent doctors, part of the flourishing community that made Breslau a European center for medical research. His relatives were friends of titans like Paul Ehrlich, the inventor of chemotherapy, and Fritz Haber, whose process for fixing atmospheric nitrogen revolutionized agriculture.

Haber was the future historian’s godfather and namesake. He was also, as Mr. Stern writes, the father of Germany’s chemical weapons program, responsible for developing poison gas weapons in World War I. Haber’s disturbing double role helps to make him one of the tutelary spirits of “Five Germanys I Have Known,” representing both the promise of German culture and the menace of German militarism. During the Nazi years, he became a symbol of another kind: despite his long, much-rewarded service to the Fatherland, not to mention his Nobel Prize, he was driven from the country by official anti-Semitism. If even a Haber could not survive in the Third Reich, what chance was there for the Sterns and hundreds of thousands of other Jews?

Mr. Stern’s description of his childhood in the Nazi years provides the book’s most dramatic and affecting moments. Six years old when Hitler seized power, he perceived the Nazi terror powerfully but confusedly. Indeed, he was not even conscious of being Jewish until he uncomprehendingly used an anti-Semitic slur during a fight with his older sister; the ensuing reprimand from his father, Mr. Stern writes, was “an astounding revelation.” As he got older, his family’s dangerous position was impossible to miss. He writes with a still smoldering outrage of the treatment he received at his Gymnasium, where most of his classmates were in the Hitler Youth. The math teacher once set as a problem, “If three Jews robbed a bank, and each got a part of the loot proportionate to their ages, how much would each get?”

The Sterns escaped from Germany in September 1938, just five weeks before Kristallnacht. It was a close call, and Mr. Stern muses that, if his father had been among the tens of thousands of Jewish men sent to concentration camps that November, his later career of engagement with Germany would have been impossible — the hatred would have been too strong. As it was, Mr. Stern remains painfully conscious of the tainted histories of so many of the scholars and public figures he would come to know.All too many names in “Five Germanys I Have Known” are accompanied by a footnote on the belated revelation of their Nazi pasts.

Once in America, Mr. Stern found a new life opening before him. He was still deeply occupied with conditions in Europe, especially once the war began, and writes poignantly of the high-school debates and editorials in which he tried to infect his classmates with enthusiasm for the Allied cause. But America was also a liberation — for one thing, from the medical career that his family traditions pointed toward. Instead, studying at Columbia with professors like Lionel Trilling and Jacques Barzun opened his eyes to the worlds of literature and history. Remarkably quickly, Mr. Stern would become their colleague, and join them in espousing the civilized liberalism of Cold War Morningside Heights. One of the best later chapters of Mr. Stern’s memoir deals with his principled resistance to the student radicals of 1968, whom he recognized as enemies of a hard-won liberal order. He writes proudly that his speech at a crucial meeting helped to defeat a faculty motion in support of the student strike.

As Mr. Stern advances in years and eminence, his book inevitably settles into a smoother, less dramatic course. Like the memoirs of a politician, “Five Germanys I Have Known” can be soporific in its politesse, full of dutiful compliments to colleagues, friends, and hosts. There are many of the latter, since Mr. Stern enjoyed to the full the privileges of the Cold War academic mandarin, giving lectures and attending conferences in Europe and around the world. The Ford Foundation, the Aspen Institute, and the Council on Foreign Relations loom larger in this book than Columbia University, just as Mr. Stern’s public interventions consume more space than his strictly historical work. Indeed, he writes about his most important book, “Gold and Iron” — a study of Bismarck’s Jewish banker Bleichroder, based on sixteen years of archival research — as a task willingly and frequently postponed in favor of speeches, interviews, and essays.

The subject of these was inevitably Germany, and how its past could be used to predict its future. Mr. Stern’s biography and scholarly expertise combined to make him on a sought-after commentator on German matters. In 1993, he spent several months advising Richard Holbrooke, the U.S. Ambassador in Berlin. His views were always firmly democratic, Atlanticist, and anti-Communist — though he takes pains to dissociate himself from the neo-conservatives, whom he regards with a combination of bien-pensant disdain and what sounds very much like plain social snobbery.

While Mr. Stern never forgot the dark strains in the German past and present, he was also a cautious optimist, convinced that Germany was on the road to true democracy. And the happy conclusion to the Cold War — which Mr. Stern, with his metropolitan contempt for Ronald Reagan and Margaret Thatcher, seems oddly shy of analyzing — proved his hopes justified. When Mr. Stern was invited to address the Bundestag on West Germany’s national holiday in 1987 — the first foreigner ever to receive the privilege — a lifetime of wary rapprochement with his native land was confirmed. “Five Germanys I Have Known” is not the most dramatic of memoirs, but it offers a historically valuable document of a happy life in difficult times.