In the old days, if you were an ambitious young Englishman looking for adventure and glory, your career path was obvious: You became a servant of the British Empire. The memoirs of George Orwell and Leonard Woolf, like the fiction of Rudyard Kipling, give a vivid sense of how exciting a young proconsul’s life could be. Back home, he was just another 22-year-old, on the bottom rung of the career ladder; in India or Burma or Malaya, he was a combination of king, judge, and general, ruling a village or even a whole province with no one to supervise him. Orwell, who wrote in “Shooting an Elephant” that his experience as a policeman in Burma “oppressed me with an intolerable sense of guilt,” recognized that even the hatred of the native population was a tribute to his power: “I was hated by large numbers of people — the only time in my life that I have been important enough for this to happen to me.”

Even today, from time to time, a young Englishman falls under the spell of the British Empire; and since he can no longer govern it, he usually decides to write about it instead. James Barr, the author of “Setting the Desert on Fire” (Norton, 382 pages, $27.95) is a fine example of the type. There is no real reason why, in order to write this book about Lawrence of Arabia, Mr. Barr had to visit the sites of Lawrence’s exploits. Yet every few chapters, Mr. Barr interrupts his narrative to tell us that, 90 years after Lawrence crossed this desert or attacked that railroad station, he was there as well. “From the police station, three hundred yards away to the west, I could see a dark hill that rises steeply out of a dusty plain,” he writes in one typical aside. “It must have been from there that, on the night of 17 September 1917, Lawrence … looked down on the station behind me, which was blazing with yellow light from within.” This is not just history writing, but channeling, or even an elevated kind of play-acting — the author imagining himself as the soldier that, a hundred years ago, he might have been.

As Mr. Barr proves, this is just the right spirit in which to approach T.E. Lawrence. For if generations of readers (and moviegoers) have imagined themselves playing Lawrence — riding on camelback through a blazing waste, leading proud tribesmen on lightning raids — Mr. Barr shows that the first person to revel in playing Lawrence of Arabia was Lawrence himself. Reporting to a friend about an attack on a Turkish troop train, he wrote, “I hope this sounds the fun it is … It’s the most amateurishly Buffalo-Billy sort of performance.” At times, he was even oppressed by the sense that he was a kind of vaudeville cowboy, and Arabia a “foreign stage on which one plays day and night, in fancy dress, in a strange language…. The whole thing is such a play, and one cannot put conviction into one’s daydreams.”

Lawrence’s desert war was “such a play,” such “fun,” because it was, to a really amazing extent, like a boy’s idea of war, all exploits and highjinks. “There aren’t any returns, or orders, or superiors, or inferiors,” he exulted. All that was back in Cairo, where the British had their headquarters, and where Lawrence worked on the intelligence staff until 1916. He had never been happy there, or popular: One of his superiors described him as “a bumptious young ass who spoils his undoubted knowledge of Syrian Arabs etc by making himself out to be the only authority on war, engineering, running HM’s ships and everything else. He put every single person’s back up I’ve met.” In fact, the 28-year-old captain was so sure of himself that he had already developed his own strategy for winning the war in the Middle East: “I want to pull [the Arabs] all together, & to roll up Syria by way of the Hijaz in the name of the Sharif.”

The Sharif in question was Husein, the ruler of Mecca, who in 1916 placed himself at the head of what was meant to be a pan-Arab rebellion against the Ottoman Empire. The British were eager to help — not just because it would be a way of striking at the Turks after the British defeat at Gallipoli, but still more because Husein represented a challenge to the Sultan’s authority as caliph, or leader of the Muslim faithful. As the rulers of tens of millions of Muslims in India, the British were worried, to what now seems a paranoid degree, by the prospect of a worldwide jihad on behalf of the Turks. (As Mr. Barr remarks, this scenario forms the plot of the classic spy novel “Greenmantle,” by John Buchan, which was published in 1916.)

But by the fall, the Arab Revolt was stalled outside the gates of Medina, and the British were beginning to realize that in Husein they had an unstable ally with delusions of grandeur. It was in this fraught moment that Lawrence seized his chance. Largely on his own initiative, he set out for Jeddah, and before long he had made himself the key liaison between the British in Cairo and Feisal, one of Husein’s sons and the commander of his northern army. Roaming the desert with Feisal’s Bedouin fighters, out of contact with his nominal superiors for weeks or months at a time, Lawrence was able to conduct a freelance war. His primary mission was to sabotage the Hijaz Railway, the only means for the Turks to supply their garrison in Medina. This meant that most of Lawrence’s actual exploits were on a very small scale — an affair of a few dozen men planting explosives under a bridge, ripping up a hundred yards of railroad track, or machine-gunning a lonely train station.

Indeed, reading Mr. Barr’s tightly focused, fast-paced account of these episodes, it is striking how minuscule Lawrence’s war remained, compared with the industrial slaughter that was going on in France. As Mr. Barr writes, the money the British spent in Arabia in a year would have paid for just seven hours of fighting on the Western Front. The human scale, too, was different. Because the Bedouin tribesmen were volunteers unused to army discipline, Lawrence had to be very sparing with his human material. The casualty rate taken for granted in France was unthinkable in Arabia, where “an individual death was like a pebble dropped in water … rings of sorrow widened out from them.”

This contrast is exactly why Lawrence became such a mythic figure, one of the few real heroes to emerge from World War I. For the vast majority of soldiers, that war was a matter of stasis, constant bombardment, futile frontal attacks, and random slaughter. Lawrence’s campaigns, on the other hand, were full of heroism and movement and mischief. In fact, there was something essentially boyish about the kind of sabotage he practiced, as another British officer readily admitted: “We could indulge in a love of destruction which had lain latent in us since we were small boys.” And the Arab Revolt was full of larger-than-life characters, some of whom would not have been out of place in the Trojan War. Auda abu Tayi, the Huwaytat chieftain who boasted of having killed 75 Arabs (he didn’t keep track of Turks), and ate the hearts of his slain enemies, was a man such as Achilles must have been.

If Mr. Barr conveys the romance of Lawrence’s war, however, he also allows us occasional glimpses of its barbarism. Because the Bedouin fought at such close range, the violence they dealt out was more personal, and at times more sadistic, than the anonymous slaughter of the trenches. Some of the locomotives Lawrence so gleefully blew up, Mr. Barr points out, were carrying women and children refugees from Medina, or sick and wounded Turkish soldiers. In one especially horrible episode, after the Arabs came across the village of Tafas, where the Turks had committed atrocities, they proceeded to massacre hundreds of Turkish prisoners. “In a madness born of the horror of Tafas,” Lawrence wrote, “we killed and killed, even blowing in the heads of the fallen and of the animals; as though their death and running blood could slake our agony.”

This elevated style is typical of “Seven Pillars of Wisdom,” Lawrence’s classic memoir, and makes that book rather cloying over the long run. It is not surprising to learn from Mr. Barr that, even during the fighting, Lawrence was already planning how he would write about it: His whole career was conceived in aesthetic terms. Mr. Barr’s achievement is to tell Lawrence’s story more clearly and objectively, helping to make sense of a complex war fought in an unfamiliar land and language.

“Setting the Desert on Fire” only glances, however, at the most important ramifications of the Arab Revolt, which continues to shape Middle Eastern politics to this day. For while the British encouraged Sharif Husein in the idea that he would be made king of all Arabia, they had no intention of ever keeping this promise. They counted on Husein’s revolt being confined to the Hijaz — the coastal area where Mecca and Medina lie. In fact, under the terms of the secret Sykes-Picot Treaty between Britain and France, the whole Arab Middle East had already been divided up between the two empires, with Syria going to the French and Iraq to the British.

Lawrence, whose idealized passion for the Arabs and their way of life led him to yearn for a free, independent Arab Empire, did all he could to undermine this cynical division of the spoils. It was largely thanks to Lawrence that the Arab forces ended up pressing as far north as Damascus, which they entered just before the British army of General Allenby, late in 1918. The result was that Husein’s dynasty, the Hashemites, ended the war claiming the right to rule all of Arabia.

In a short epilogue, Mr. Barr shows the reckless and shortsighted way the British met these claims. Two of Husein’s sons were made kings of the puppet states the British created in the Arab lands: Abdullah was given Jordan, where his dynasty still reigns, and Feisal was placed on the throne of Iraq, where the monarchy was overthrown in 1958. Both these dynasties, like the states they ruled, were entirely arbitrary creations, imposed by the British in defiance of cultural and political logic. Even Feisal acknowledged that “there is still — and I say this with a heart of sorrow — no Iraqi people, but unimaginable masses of human beings, devoid of any patriotic idea … prone to anarchy and perpetually ready to rise against any government whatever.”

As these words show, not much has changed in Iraq. Today, when America tries to pacify a country divided between Shiites, Sunnis, and Kurds, it is reaping what the British sowed. A similar story could be told of Palestine, where Britain’s failure to reconcile its promises to the Arabs with the commitment it made to the Jews, in the Balfour Declaration, helped to create the unending Arab-Israeli conflict. Even Osama bin Laden, Mr. Barr shows, lists the Sykes-Picot agreement as one of his major historical grievances.

Seen from today’s perspective, then, Lawrence’s story looks less like a chivalric romance than like a case of imperial arrogance run amok. Only by taking advantage of the incredible carelessness and cynicism of the men who ran the British Empire was a junior officer able to remake the Middle East according to his own whims. It is enough to make one glad that there is no more British Empire, even if it means that there will never be another Lawrence of Arabia.