Sir John Keegan, an Englishman widely considered to be the pre-eminent military historian of his era and the author of more than 20 books, including the masterwork “The Face of Battle,” died Thursday at his home in Kilmington, England. He was 78.

His death was announced in The Telegraph, where he had served as the defense editor. No cause of death was given, though Con Coughlin, the paper’s executive foreign editor, said in an email that Keegan had died after a long illness.

Keegan never served in the military. At 13 he contracted orthopedic tuberculosis and spent the next nine years being treated for it, five of them in a hospital, where he used the time to learn Latin and Greek from a chaplain. As he acknowledged in the introduction to “The Face of Battle,” he had “not been in a battle, nor near one, nor heard one from afar, nor seen the aftermath.”

But he said he learned in 1984 “how physically disgusting battlefields are” and “what it feels like to be frightened” when The Telegraph sent him to Beirut to observe the civil war in Lebanon.

Keegan’s body of work ranged across centuries and continents and, as a whole, traced the evolution of warfare and its destructive technology while acknowledging its constants: the terrors of combat and the psychological toll that soldiers have endured.

He had a keen interest in the United States, receiving a visiting fellowship at Princeton, writing meditations on North American wars and briefing President Bill Clinton in preparation for the 50th anniversary of the Normandy invasion in 1994.

Cultural questions

Keegan was particularly concerned with the cultural roots of war, asking, “Why do men fight?” In his classic 1993 study “A History of Warfare,” he argued that military conflict was a cultural ritual from which the modern notion of total war, like in World War I, had been an aberration.

His topics included King Henry V of England, Napoleon and the military machine of Hitler, but he also grappled with warfare in the nuclear age, concluding in “The Face of Battle” that total war was now almost unthinkable. “The suspicion grows that battle has already abolished itself,” he wrote.

In “The Iraq War,” published in 2004, he followed the technological revolution in warfare with the introduction of computer-guided “smart” weapons. He also rendered a political judgment, concluding — with the war still new and yet to be transformed by sectarian conflict and the surge of U.S. troops — that the invasion to overthrow Saddam Hussein was justified.

Probably none of his books was more admired than “The Face of Battle.” The Cambridge historian J.H. Plumb called it “so creative, so original” and a “brilliant achievement.” A huge publishing success, it launched Keegan’s career as a popular historian.

He examined three battles in the book: Agincourt in 1415, Waterloo in 1815 and the Somme in 1916, all in the northeast corner of France and all involving the English. His tale was somber and compelling on what happens in the heat of battle, including the execution of prisoners.

He was not above a personal note. Describing the horrors at the Somme, where his father was gassed, he appears to grow downhearted, pausing to reflect on how the war’s shadow lingers even 70 years later.

He speaks of “the military historian, on whom, as he recounts the extinction of this brave effort or that, falls an awful lethargy, his typewriter keys tapping leadenly on the paper to drive the lines of print, like the waves of a Kitchener battalion failing to take its objective, more and more slowly toward the foot of the page.”