The United States might claim a broader democracy than those that prevailed in Europe. On the other hand, European states mobilized their populations with an efficiency that dazzled some Americans (notably Theodore Roosevelt) and appalled others (notably Wilson). The magazine founded by pro-war intellectuals in 1914, The New Republic, took its title precisely because its editors regarded the existing American republic as anything but the hope of tomorrow.

Yet as World War I entered its third year—and the first year of Tooze’s story—the balance of power was visibly tilting from Europe to America. The belligerents could no longer sustain the costs of offensive war. Cut off from world trade, Germany hunkered into a defensive siege, concentrating its attacks on weak enemies like Romania. The Western allies, and especially Britain, outfitted their forces by placing larger and larger war orders with the United States. In 1916, Britain bought more than a quarter of the engines for its new air fleet, more than half of its shell casings, more than two-thirds of its grain, and nearly all of its oil from foreign suppliers, with the United States heading the list. Britain and France paid for these purchases by floating larger and larger bond issues to American buyers—denominated in dollars, not pounds or francs. “By the end of 1916, American investors had wagered two billion dollars on an Entente victory,” computes Tooze (relative to America’s estimated GDP of $50 billion in 1916, the equivalent of $560 billion in today’s money).

That staggering quantity of Allied purchases called forth something like a war mobilization in the United States. American factories switched from civilian to military production; American farmers planted food and fiber to feed and clothe the combatants of Europe. But unlike in 1940-41, the decision to commit so much to one side’s victory in a European war was not a political decision by the U.S. government. Quite the contrary: President Wilson wished to stay out of the war entirely. He famously preferred a “peace without victory.” The trouble was that by 1916, the U.S. commitment to Britain and France had grown—to borrow a phrase from the future—too big to fail.

Tooze’s portrait of Woodrow Wilson is one of the most arresting novelties of his book. His Wilson is no dreamy idealist. The president’s animating idea was an American exceptionalism of a now-familiar but then-startling kind. His Republican opponents—men like Theodore Roosevelt, Henry Cabot Lodge, and Elihu Root—wished to see America take its place among the powers of the earth. They wanted a navy, an army, a central bank, and all the other instrumentalities of power possessed by Britain, France, and Germany. These political rivals are commonly derided as “isolationists” because they mistrusted the Wilson’s League of Nations project. That’s a big mistake. They doubted the League because they feared it would encroach on American sovereignty. It was Wilson who wished to remain aloof from the Entente, who feared that too close an association with Britain and France would limit American options. This aloofness enraged Theodore Roosevelt, who complained that the Wilson-led United States was “sitting idle, uttering cheap platitudes, and picking up [European] trade, whilst they had poured out their blood like water in support of ideals in which, with all their hearts and souls, they believe.” Wilson was guided by a different vision: Rather than join the struggle of imperial rivalries, the United States could use its emerging power to suppress those rivalries altogether. Wilson was the first American statesman to perceive that the United States had grown, in Tooze’s words, into “a power unlike any other. It had emerged, quite suddenly, as a novel kind of ‘super-state,’ exercising a veto over the financial and security concerns of the other major states of the world.”