Phillips O'Brien
Based on Wikipedia: Phillips O'Brien
The Historian Who Rewrote World War Two
What if everything you learned about how the Allies won World War Two was wrong?
Not slightly off. Fundamentally mistaken. What if the decisive factor wasn't the great land battles—not Stalingrad, not D-Day, not the push through France and into Germany—but something far more sprawling and invisible to most histories?
This is the argument that Phillips O'Brien has spent his career building, and it has made him one of the most provocative military historians working today. His thesis is deceptively simple: the war was won in the air and at sea, across what he calls an "Air-Sea Super Battlefield" stretching thousands of miles. The land battles that fill our textbooks? They were important, yes, but they were consequences of this larger struggle, not its drivers.
From Wall Street to War Studies
O'Brien's path to becoming a military historian took an unusual detour through high finance. Born in 1963 and raised in Boston, Massachusetts, he graduated from Trinity College in Connecticut and then spent two years working on Wall Street. The experience apparently convinced him that analyzing markets was less interesting than analyzing conflicts between nations.
He crossed the Atlantic to pursue graduate work at Cambridge University, where he studied at Pembroke College as both a Mellon Research Fellow in American history and a Drapers Research Fellow. There, he fell under the influence of Zara Steiner, herself an American-born historian who had made her career in Britain studying international relations and diplomacy. O'Brien would follow a similar transatlantic trajectory.
His doctoral dissertation examined the interplay between British and American naval policy during the early twentieth century—specifically the period from 1900 to 1936. This might sound like a narrow academic exercise, but it laid the groundwork for everything that followed. Understanding how two great naval powers thought about sea control, how they built their fleets, how they calculated threats and opportunities—this became the lens through which O'Brien would eventually reexamine the entire Second World War.
The Scottish Years
After Cambridge, O'Brien took a position at the University of Glasgow, where he did something unusual for an American historian: he became the director of the Scottish Centre for War Studies. Scotland might seem like an odd place for an American to plant his flag in military scholarship, but British universities have long traditions in strategic studies that American institutions often lack.
At Glasgow, O'Brien edited two important academic volumes. The first, published in 2001, examined how technology had transformed naval combat throughout the twentieth century. The second, appearing in 2004, explored the Anglo-Japanese Alliance—a treaty relationship that lasted from 1902 to 1922 and fundamentally shaped the balance of power in East Asia.
The Anglo-Japanese Alliance is one of those historical agreements that most people have never heard of but that shaped the world we live in. When Britain and Japan signed their alliance in 1902, it was the first time a European great power had entered into an equal military partnership with an Asian nation. The alliance deterred Russia in the Pacific, freed up British naval resources for European waters, and gave Japan the confidence to challenge Russian expansion in Manchuria. When Britain chose not to renew the alliance in 1922—partly under American pressure—it set Japan on a path of diplomatic isolation that would eventually lead to Pearl Harbor.
O'Brien's immersion in these questions of naval power and alliance politics prepared him for his most ambitious work.
The Air-Sea Super Battlefield
In 2015, O'Brien published the book that would make his reputation: "How the War Was Won: Air-Sea Power and Allied Victory in World War II." The title alone was a provocation. Most histories of the Second World War emphasize the great land campaigns. The Eastern Front, where the Soviet Union and Nazi Germany fought the largest and bloodiest battles in human history. The North African campaign. The invasion of Italy. D-Day and the liberation of Western Europe.
O'Brien didn't deny the importance of these battles. But he argued that they were downstream of a more fundamental contest—one that determined whether armies could be equipped, supplied, and transported in the first place.
Think about it this way. Before a German tank could fire a shell at a Soviet position, an enormous chain of industrial processes had to occur. Iron ore had to be mined. Steel had to be forged. The tank had to be manufactured, then transported by rail or road to the front. The crew had to be trained. Fuel had to be refined and delivered. Ammunition had to be produced and shipped.
At every link in this chain, Allied air and sea power could intervene. Bombers could destroy the factory. Submarines could sink the ore ship. Fighters could strafe the rail yard. Long-range aircraft could hunt the fuel convoy.
O'Brien meticulously calculated how each major combatant allocated its military production. How much went to armies? How much to navies? How much to air forces? His numbers told a striking story. The Allied powers—particularly the United States and Britain—devoted enormous resources to building aircraft and ships. The Axis powers—Germany, Japan, and Italy—tried to compete but fell further and further behind.
The result was what O'Brien called the "Air-Sea Super Battlefield"—a vast arena of combat stretching across oceans and continents where the Allies gradually established dominance. Once they controlled this battlefield, they could strangle Axis war production. German factories were bombed. Japanese merchant ships were sunk. Italian ports were blockaded. The Axis armies kept fighting, but they were fighting with one hand tied behind their back, starved of the equipment and supplies they needed.
The Critics Respond
Academic reviewers recognized immediately that O'Brien had written something significant. Talbot Imlay, writing in the Journal of Modern History, called it "provocative" and "revisionist history at its best." But not everyone was fully convinced.
Nicholas Murray, reviewing the book for the Naval War College Review, offered a more nuanced assessment. He noted that O'Brien wasn't really revising the traditional history so much as "revising the revisionists"—scholars had been debating the relative importance of air, sea, and land power for decades. Murray appreciated O'Brien's detailed analysis showing how much damage the Allies inflicted on Axis capabilities, but he wasn't certain this damage was truly decisive rather than merely contributory.
Still, Murray found one of O'Brien's insights particularly relevant for contemporary military planners. O'Brien argued that the way to win a modern war is to prevent your enemy from moving—to control the spaces through which armies, supplies, and equipment must travel. This has obvious implications for American strategists contemplating potential conflicts with China in the South China Sea or with Russia in the Baltic region. Whoever controls the air and sea can choke off an opponent's ability to project power.
The Man Behind Roosevelt
O'Brien's next major book, published in 2019, shifted from strategic analysis to biography—but biography with a provocative thesis. "The Second Most Powerful Man in the World" told the life story of Admiral William Leahy, who served as chief of staff to President Franklin Roosevelt during World War Two.
Leahy is one of those figures who appears in countless photographs of the war's key moments but whom most people cannot identify. He's the officer standing slightly behind Roosevelt at Yalta, at Quebec, at Cairo. Always present, rarely remembered.
O'Brien argued that this obscurity was deeply misleading. Leahy, he contended, exercised more influence over American wartime decisions than any figure except Roosevelt himself—hence the book's title. This was a bold claim. What about George Marshall, the Army chief of staff whom historians routinely celebrate as the architect of Allied victory? What about Ernest King, the famously cantankerous chief of naval operations? What about the field commanders—Eisenhower, MacArthur, Nimitz?
O'Brien built his case through Leahy's unique relationship with Roosevelt. The president trusted Leahy implicitly. They had known each other for decades—Leahy had commanded Roosevelt's presidential yacht before the war. Roosevelt made Leahy his personal chief of staff and de facto chairman of the Joint Chiefs, giving him access to every major decision.
According to O'Brien, Leahy shaped some of the war's most consequential choices. He pushed for giving equal or even higher priority to the Pacific war against Japan rather than the conventional wisdom of defeating Germany first. He opposed an early Allied invasion of Europe in 1943, fearing it would be a bloodbath—a judgment that proved correct when the eventually better-prepared D-Day invasion nearly faltered a year later.
The book's later chapters examined Leahy's more difficult relationship with Roosevelt's successor, Harry Truman. Leahy was instinctively non-interventionist, skeptical of America's expanding global commitments in the early Cold War. He and Truman were never as close as he and Roosevelt had been.
A Biography Without Sources?
Reviewers generally praised the book while noting one significant limitation. Craig Symonds, writing for HistoryNet, observed that O'Brien credited Leahy with far more influence than Henry Adams had in his 1985 biography "Witness to Power." But Symonds also noted that O'Brien often had to rely on circumstantial evidence because primary sources documenting Leahy's actual role were scarce. When you're the power behind the throne, you don't necessarily leave a paper trail.
Matthew Wayman in Library Journal called it an "excellent biography of a significant but neglected figure," though he noted O'Brien's tendency to avoid criticizing his subject. Steve Donoghue, reviewing for the Christian Science Monitor, welcomed the book as "an overdue first-rate telling" of a man who had "more authority than celebrity"—the quiet commander in the background of every famous photograph.
The Move to St Andrews
In 2016, O'Brien moved from Glasgow to the University of St Andrews, Scotland's oldest university and one of Britain's most prestigious. There, he became professor of strategic studies—a position that places him at the intersection of history and policy.
This dual role—scholar and strategic analyst—has made O'Brien an increasingly visible commentator on contemporary military affairs. He gave expert testimony to the Scottish Affairs Select Committee of the British House of Commons in 2012, analyzing what would happen to Britain's nuclear weapons if Scotland voted for independence and left the United Kingdom. The nuclear submarine base at Faslane, on the Clyde near Glasgow, would presumably have to be relocated to somewhere in England—a logistically complex and politically explosive proposition.
The Strategists
O'Brien's most recent book, published in 2024, is his most ambitious yet. "The Strategists" examines five leaders—Winston Churchill, Joseph Stalin, Franklin Roosevelt, Benito Mussolini, and Adolf Hitler—asking how war shaped them and how they in turn shaped war.
This is a crowded field. Countless books have been written about each of these men individually, and many have compared their leadership styles. What O'Brien brings to the subject is his distinctive focus on strategic decision-making: how leaders understood air power, sea power, and the emerging technologies that would determine victory or defeat.
Why This Matters Now
O'Brien's work has taken on new relevance as great power competition returns to international politics. His arguments about the Air-Sea Super Battlefield speak directly to current debates about how the United States should prepare for potential conflicts with China or Russia.
Consider the Taiwan Strait. If China were to attempt an invasion of Taiwan, success would depend on controlling the air and sea spaces between the mainland and the island. American strategists debate whether enough ships and aircraft could be brought to bear quickly enough to prevent a Chinese fait accompli. O'Brien's historical analysis suggests that whichever side controls those spaces—whichever side can prevent the other from moving—will ultimately prevail.
Or consider the war in Ukraine, which has renewed interest in questions O'Brien has studied for decades. How does air power interact with ground combat? What happens when neither side can achieve air superiority? How do supply lines and logistics determine what armies can actually accomplish?
These aren't academic questions anymore. They're questions that military planners and political leaders are wrestling with right now. And Phillips O'Brien, the Wall Street refugee who became one of Britain's leading strategic historians, has spent his career providing the historical context to think them through.
A Scholar's Journey
Looking at O'Brien's career, certain patterns emerge. He has consistently gravitated toward questions that challenge conventional wisdom. His first book questioned standard accounts of early twentieth-century naval policy. His major work on World War Two questioned the entire historiographical tradition that privileged land battles. His Leahy biography questioned who really wielded power in wartime Washington.
This contrarian streak is valuable in historical scholarship, where established narratives can calcify into received wisdom that no one thinks to question. O'Brien questions. He digs into production statistics and shipping tonnages and the unglamorous details of logistics. He reads the footnotes and challenges the assumptions.
The result is a body of work that has forced other scholars to reckon with arguments they might prefer to ignore. Even his critics acknowledge that he has raised questions that demand answers. And in a field as well-trodden as World War Two history, that's no small achievement.