“Very early,” writes the distinguished historian John Lukacs in the introduction to A Thread of Years, his 20th—and certainly his most unusual—book, “I was inspired by the recognition of the inevitable overlapping of history and literature, that not only what a Balzac but what a Jane Austen described—indeed, what they dealt with—belong not only to the history of literature, but to the veritable history of a period: that is, of a place and a time. Bath in 1816 differed from Bath in 1803, New York in 1920 from New York in 1915, and these are matters for a historian to think about and to research and to describe. Of course, we must keep in mind how dramatic changes may obscure the essential human condition, through which continuation exists together with change. I do not mean political conditions but the human atmosphere: the mental, rather than the external, climate of how certain people were inclined, how and what they were wanting and thinking and perhaps believing.”

The subtlety, the intimacy of such a pursuit, pushes the historian close to the boundary that separates him from the novelist, and, although Lukacs insists that A Thread of Years is not a novel, it is not not a novel, either. And, indeed, history and the novel have many things in common, among them what Lukacs calls “their necessary recognition of potentiality, together with actuality: of what happened with what could have happened. Historicity is what makes a novel plausible, and that plausibility must be apparent. This is why not only Old Goriot or The Scarlet Letter but The Great Gatsby are essentially historical novels. (Yes: Gatsby & Co. did not exist. But readers of that novel must know that there were people and manners and places like that at that particular time in American history. The quality of that plausibility is what matters—the understanding that not only Gatsby but what happened to him could have happened, then.)”

Such concerns have led Lukacs to try to write a work of history—and of fiction—that communicates the nearly incommunicable, the stuff of the past that everyone who has experienced it knows, and rarely utters: the difference in the sense of light, for instance, in the Bois de Boulogne during the famously lush summer of 1914 and the jaded summer of 1927.

But, in Lukacs’s book, these shimmers and scents and fading echoes are at the service of a larger theme: “That theme is the decline of a particular civilization, and the decline of the ideal of the gentleman; two inseparable matters. In 1901 the British and American empires were the greatest powers in the world. On the map of the globe the British Empire was greatest; but the center of gravity had already shifted across the Atlantic, and was moving westward. The threat to the Atlantic predominance was represented by Germany, with the result