Willkie’s trip around the world is at the heart of The Idealist. The journey is unjustly forgotten today, but at the time it was heralded as a major political event. This was late summer of 1942, the darkest days of the war, when the world waited for the U.S. to fully join the fight, before it was clear the Allies would win. Willkie’s trip lifted spirits, but also challenged Americans to see the world anew.Any number of scenes from his travels might grab a reader’s attention. In Egypt he toured the front west of Cairo and announced a turning point in the war at El Alamein. In Beirut he got an unvarnished picture of colonialism from Arab and Lebanese nationalists and jousted with a recalcitrant and haughty Charles de Gaulle, who refused to compromise French interests in the region. Jerusalem brought him face to face with both the Palestinians and the Zionists and the bitter impasse that would do so much to shape the postwar world. In Iran, Willkie gave the young Shah his first ride in an airplane. The gesture, meant to reassure the Iranians of American goodwill, foreshadowed the Cold War paternalism that would bring so much calamity to both countries.Previously undiscovered Soviet sources helped me bring to life Willkie’s travels in war-ravaged Russia, where he debated political economy with a factory worker, visited the front west of Moscow, and encountered Joseph Stalin. The two leaders circled each other warily, each trying to make the vast, bloody drama of the besieged Soviet Union serve their own interests.Willkie fell hard for Chiang Kai-Shek’s China. His rumored dalliance with Madame Chiang is the salacious highlight, but the Chiangs’ nationalist anti-imperialism gave him a glimpse of the non-aligned world to come and the incipient politics of what we call the Global South. Willkie’s much heralded but long forgotten speech in Chongqing tried to alert the Allies to this rising force in world affairs and to redefine the war as a battle for freedom from empire.The trip sparked new conflicts with rivals old and new. Winston Churchill, irked by Willkie’s frank criticism of colonialism, responded to the trip by taking the trouble to announce to the world that Britain did not fight to see the empire destroyed. Roosevelt bristled at Willkie’s independence, but admired his gumption. The book follows their differences over the shape of the future United Nations—as well as an aborted collaboration: not long before Willkie’s untimely death in 1944 the two leaders launched a back channel discussion about forming a new political party to unite the nation’s liberals.Beyond these particular scenes, I’d like to find readers who appreciate the lived history of ideas. The story of Willkie’s jaunt around the world enlivens the strange career of a concept. The idea of global interdependence, his “one world,” has become both a common sense cliché and a much-maligned expression of utopian unity. I close the book with an account of one world’s long reach across the twentieth century. The point is not to champion the idea, but to rediscover the dilemmas it still holds for us today.The Idealist is a strange and ambivalent tale, in a way. The book is a history of an idea that’s self-evident: it’s never been more obvious how technology, greenhouse gasses, markets, and the threat of pandemics connect us all. But it’s also a history of failure. The vision of global governance Willkie and many other midcentury internationalists favored was partially realized, but in a diluted fashion, and has been in retreat ever since. The postwar years, the historian David Reynolds argued two decades ago, could be summed up as a story of “one world, divisible.”Willkie offered a geopolitical vision of a world in need of new maps and a new kind of global imagination. It was an idealistic vision, of a planet united in cooperation through a new world body designed to succeed where the League of Nations had failed. But it was strategic as well, envisioning the United States cooperating with the Soviet Union, championing decolonization, and managing a reinvigorated network of global trade. In his version of the future, America remained indispensable, not as the proprietor of a new empire, but as the guarantor of the freedom and equality imagined as the country’s birthright.This was a treacherous path. Willkie was trying to tiptoe between two nationalisms—a lingering parochial hawkishness on the right and an emerging expansionary liberal nationalism that he both disputed and sometimes epitomized. In the end, Willkie revealed Americans’ contorted and conflicted feelings about the world at large.For 75 years after World War II, Americans did embrace a global role, but it was too often one forged from a new kind of imperial vision. From the Cold War to the War on Terror, American global influence has been both benevolent and despotic—depending where you look—but always comfortable in its assurance that American dominance was indispensable to any kind of just world order. Now, however, that faith is in retreat.Willkie took his trip at a hinge moment in the history of the twentieth century. The globe swung between a world shaped by European empire and a world shaped by American-led global capitalism. Now, with American power on the wane, we are living through another hinge moment. The 21st century will be shaped by a host of new factors: Chinese state capitalism, Russian authoritarianism, simultaneously rising prosperity and inequality, and a new global upsurge of nationalism in the face of climate-fueled migration and global pandemics. The United States can no longer pretend to “lead” the rest of the world. Willkie’s journey asks us to think about how we will live in the world rather than dominate it.