American soldiers who went to war became known as dough-boys, possibly because their long marches left them covered in dust. Here, the Seventh Regi- ment shows the colors in New York City.Corbis

Some years ago, when I set out to write a book about America and the First World War, I made the rounds of local bookstores to see what was out there already. I was pretty well prepared to confront a dearth of material on the American role in the Great War; that was, indeed, one of the reasons I had chosen the subject. What really surprised me, though, was how little there was to be found on any facet of the war. The stores’ history sections contained bookcases of volumes about the Civil War and World War II, but only—if I was lucky—a shelf of World War I books sandwiched in between. And almost all of those were British imports.

So I turned to vintage bookshops, hoping that perhaps, once upon a time, more had been written and published in this country on a topic formerly known simply as the world war. I quickly discovered that more had. Much, much more. No one seemed to want any of it, either; eventually I amassed, for a pittance, a library of hundreds of volumes published between 1914 and 1930 or so, all of them long since out of print.

And there was still more: In flea markets and junk shops, I came across stacks of Great War–era 78s, reams of wartime sheet music, posters, pieces of uniforms, Army-issued handbooks and prayer books. Most of all, it seemed that wherever I went, in every part of the country, I found monuments and memorials to the war and to the men and women who went off to fight it. If an American town anywhere was a thriving concern in 1917, I would bet it put up something—a plaque, a statue, a marble bench, an arch—after November 11, 1918. Even places that don’t have anything commemorating the Civil War or World War II have something, in my experience, for World War I.

The people who commissioned those monuments—and who read those books, played those records, bought that sheet music—weren’t thinking short-term. They believed the Great War would remain great in the American consciousness for eternity, that future generations would sooner forget Bunker Hill and Lookout Mountain than Belleau Wood and the Argonne Forest. They believed, more than anything, that it was Americans who had won that war. How surprised they would be, less than a century later, to find all those old books languishing unread and to discover that few Americans are writing new ones, because Americans now largely believe—when they think about the subject at all—that their country just didn’t do all that much in the First World War.

And those Americans of yore would be justified in their surprise. While it is certainly too much to say the Yanks won the Great War by themselves, it is indisputable that the Allies would not—could not—have won the war without the United States. Although America was not, at that time, widely regarded as a world power, the nation made three indispensable contributions to the Allies’ victory over the Central Powers in World War I.

1914–16: Money and Materiel

When Europe collapsed into war in the summer of 1914, many Britons expected that the United States would soon enter the conflict on their side; although the U.S. wasn’t a British dominion—as were Canada, Australia, and New Zealand, all of which declared war on Germany when Britain did—there was a strong belief that the spirit of Anglo-American kinship would move the former colony to join the fight anyway. No one, not even Germans, dared imagine that America might enter the war on Germany’s side, despite the strong economic ties and generally friendly relations the two nations enjoyed (going back to the Revolutionary War, when many German officers volunteered for the Continental Army), and despite the fact that in 1914 more Americans traced their ancestry to Germany than to any other country (which is still true in 2014). The best the Central Powers could hope for was that America might sit this one out.

And it did, at the outset. Most Americans favored neutrality, and President Woodrow Wilson obliged them. He even adopted a rather muscular definition of neutrality, which he articulated to Congress on August 19, 1914:

The United States must be neutral in fact, as well as in name, during these days that are to try men’s souls. We must be impartial in thought, as well as in action, must put a curb upon our sentiments, as well as upon every transaction that might be construed as a preference of one party to the struggle before another.

At the same time, though, no one—at least no one in a position to make policy—believed that neutrality meant you couldn’t do business with both sides. Quite the contrary: in the America of 1914–16, it was regarded as a violation of neutrality for the government to prevent Americans from trading with any of the combatant nations. In theory, American manufacturers were free to sell munitions to the highest bidders, whoever they might be.

But only in theory. The British had the largest and most powerful navy in the world in 1914—they really did rule the waves back then—and quickly established an impenetrable blockade against the Central Powers, one that held up until the armistice. So while Americans were free to sell all the war materiel they liked to Germany, Germany had no way to take delivery and, therefore, little interest in buying. Fortunately for U.S. manufacturers, the Allies had a tremendous appetite for American arms and armaments: the United Kingdom, for example, spent about half—half—its war budget in the United States. Arthur Guy Empey, an American who served with the British army in France, recounted in his best-selling 1917 memoir, Over the Top, seeing in Flanders “a never-ending stream of men, supplies, ammunition, and guns pouring into the British lines,” among them a great convoy of steam-powered tractors pulling enormous howitzers.

When one of these caterpillars would pass me with its mighty monster in tow, a flush of pride would mount to my face, because I could plainly read on the name plate, “Made in U.S.A.” … Then I would stop to think how thin and straggly that mighty stream would be if all the “Made in U.S.A.” parts were withdrawn.

Britain’s war budget, as you might imagine, was quite large; even half of it was much more than the British could finance on their own. “Neutral” American bankers, though, had plenty of cash on hand, and were happy to lend Britain all it needed (at healthy interest rates, naturally). And not just Britain: France borrowed so heavily from U.S. banks (primarily the House of Morgan) that repaying the loans nearly destroyed its economy after the war. And so, from the outset of hostilities, America and the Allies had a symbiotic relationship that was essential to the course of combat. Without American war materiel—and the American money to purchase it—the Allies could never have come close to matching the productive capacity of Germany, the world’s leading industrial power at the time; if they hadn’t, they would have lost the war well before 1917.

Germany, meanwhile, unable to trade with the United States, employed more-surreptitious methods to curtail the Allies’ advantage. One was sabotage, dispatching secret agents to destroy American-made war materiel before it could be delivered to Britain or France. (In the most notorious incident, in 1916, saboteurs at a munitions depot near Jersey City set off an explosion—felt in Philadelphia, heard in Maryland—that destroyed hundreds of tons of armaments bound for Europe.) Another was unrestricted submarine warfare against ships thought to be carrying munitions to the Allies. It was these U-boat attacks that ultimately drove Wilson to reconsider his policy of neutrality and to prevail on Congress to declare war against Germany in April 1917.

1917: The Menace of Manpower

Given the role that German U-boats played in drawing the United States into the war, many Americans believed at first that their country’s main military contribution would be naval. Within weeks, however, Britain and France would send officials to Washington to persuade the War Department that what the Allies really needed was men in the trenches, and lots of them. Two and a half years of trench warfare had taken a terrible toll on their ranks.

General John J. Pershing, the commander of the American Expeditionary Forces (AEF), was fine with that—with some caveats. For one thing, the United States didn’t have much of an army yet—fewer than 200,000 men when the country entered the war—and would need time to build one. And more time to train it. Pershing made clear that he would not allow Americans to fight until they were ready, and he planned to be conservative in making that judgment. When they were ready, they would fight only in American divisions, under American commanders. Pershing didn’t want them parceled out to British and French units as replacements; he knew that colonial and dominion soldiers were often put in indefensible positions to distract the enemy from British and French troops and, as a result, took very high casualties.

But if the British and French were unhappy about Pershing’s decrees—and they were—they could take comfort in the number of troops the general expected to raise: 4 million. They spread that figure around, hoping to foment panic in the German high command.

It worked. The Central Powers—which, in Europe, at least, really meant the Germans, as the Austro-Hungarian army had proved itself largely ineffective since the war’s earliest days—had been surrounded and outnumbered from the start. Still, they had managed to hold their own, because the margin of difference (at least on the western front) wasn’t that great, and the Germans had superior industry, technology, and—most historians would concede—soldiers and generals. But 4 million fresh American troops would surely tip the balance in the Allies’ favor, and the Germans knew it.

They also knew—besides its saboteurs, Germany had an excellent network of spies in America—that those doughboys wouldn’t reach France for a while. Russia was teetering; knocking the Russians out of the war would enable Germany to shut down the eastern front and transfer half a million seasoned soldiers to France before the Americans arrived in force. This would allow German troops to launch a massive offensive and win the war in the nick of time.

Which they did—except for that last part. It took Germany longer than expected to secure a peace treaty with Russia, and by the time it did, on March 3, 1918, the fledgling AEF already had several fighting divisions—about 25,000 men apiece—in France. Anxious to get the offensive under way before even more Americans showed up, Germany launched its attack less than three weeks later. That was barely enough time to get all the troops in place, and not nearly enough time to establish adequate supply lines or even to plan the offensive with any precision. Yet the Germans pushed ahead, gambling that the advantages of speed and surprise would compensate for these shortcomings.

The Spring Offensive of 1918, as it is now remembered, succeeded magnificently—too magnificently, really. The Germans got so far ahead of their own supply lines that they were soon beset by crippling shortages. What’s more, they overran their initial objectives so quickly that they found themselves floundering, with no idea what, exactly, to do next. While it appeared on the surface to have paid off handsomely, that great gamble the Germans had taken because of the threat of 4 million fresh doughboys actually left them confused, directionless, hungry, and ill-equipped—vulnerable.

And the first of those doughboys were already in a position to exploit that vulnerability.

1918: Military Might

The Germans, seeing their Spring Offensive falter, held out one last hope: that they might inflict so much damage upon the untested American Expeditionary Forces in battle that the doughboys could lose their will to fight or even succumb to defeat. And indeed, in the two armies’ first major encounter, on April 20 at Seicheprey, in northern France, German shock troops caught the Americans by surprise and quickly took the town, along with nearly 200 prisoners. But within hours, the Americans rallied and recaptured it; then U.S. troops went on the attack and drove the Germans out of Cantigny on May 28 and, a few days later, repelled the Germans at Chateâu-Thierry. The Germans moved into Belleau Wood, a dense, strategically located forest nearby, where they had formidable defenses. The French, reluctant to follow the Germans into such a place, asked Pershing to send in an American division to root them out; Pershing, perhaps unaware of how dangerous the position was, dispatched the Second Division, which included two regiments of marines. The battle lasted nearly three weeks and claimed nearly 10,000 American casualties. (More marines were killed or wounded at Belleau Wood than in the service’s entire 143-year history to that point.) But in the end, it was a grand triumph for the American forces—militarily and psychologically.

The Germans regrouped and launched a vast assault across the Marne River, where French and British troops had stopped them four years earlier. This time, they made great advances—everywhere except at the critical western end of the line, only about 40 miles from a panicked Paris, where the American Third Division stopped them cold at the river’s edge. (To this day, the division is known as “The Rock of the Marne.”) It was the Germans’ last offensive of the war: three days after they failed to move the Rock of the Marne, American and French troops launched a counteroffensive that would ultimately drive them out of the area entirely. The Germans would remain on the defensive until the war ended.

Though they could no longer win the war outright, they still hoped—quite reasonably—to achieve a stalemate, dragging out the fighting and weakening their enemies’ will to the point that they could dictate the terms of a cease-fire. Both sides expected the war to rage well into 1919, especially considering how fiercely the Germans clung to every bit of ground and how dearly they made the Americans pay for every inch. Then, in early September 1918, the Expeditionary Forces caught the Imperial German Army by surprise at Saint-Mihiel, in northeastern France, and captured more than 200 square miles—including many towns the Germans had occupied for four years—in just two days. The American troops followed this with their greatest offensive of the war, the Meuse-Argonne, to the west. Some 1.2 million Americans fought there; by the time the battle ended, at 11 a.m. on the 11th of November, 26,277 of them had been killed. It remains, to this day, the deadliest battle in American history—but it was also a great American victory, and a crucial one. As much as anything else that fall, Meuse-Argonne forced Germany to plead for an armistice.

This isn’t to say the U.S. won the war on its own. But America’s three major contributions, going back to 1914, unquestionably guided the war’s course. Without the United States, the Allies, at best, would have fought to a stalemate.

So why have Americans forgotten the first worldwide war, and their pivotal role in it? The answer starts with an uncomfortable truth: Although it ended in victory, World War I proved to be more of a traumatic experience than Americans were prepared to deal with. In just 19 months, the United States lost more than 116,000 men in the War to Make the World Safe for Democracy; many more would die in later years slowly and painfully, from the lingering effects of bullets, shrapnel, poison gas, and what was then called shell shock.

For a while, it seemed, Americans comforted themselves by staging parades, building monuments, and otherwise honoring their doughboys, dead and living. But hard times can make people introspective, and by the onset of the Great Depression, many Americans found themselves wondering just what, exactly, all those young men had died for; it was obvious, by then, that much of the world was still not safe for democracy, and might never be. Americans no longer cared to talk or think about the Great War; even veterans felt that way, as I discovered while interviewing dozens of them (ranging in age from 101 to 113) more than eight decades after the armistice. Americans who lived through the Great War, typically born and raised in meager circumstances, tended to believe that everyone had troubles, and you shouldn’t attract attention to your own. American authors, who had cranked out books on the war for a while after it ended, stopped writing about it, ceding the history of America’s role to anyone else who cared to address it.

That turned out to be the British, who never tired of writing about the trauma of the Great War, and who alone continued to do so in Americans’ mother tongue. Unfortunately for Americans, many in Britain were still upset over the U.S. refusal to enter the war in 1914 and, taking a dim view of the Expeditionary Forces’ accomplishments in 1917 and 1918, portrayed its generals as incompetent, its officers as ineffective, and its soldiers as poorly trained, ill-disciplined, and inconsequential. (Some British historians still hold this view today.) The Americans, these skeptics held, arrived only near the end, too late to do anything but claim credit they didn’t deserve. Many Americans—even those who had lost someone Over There—seem to have taken that to heart and accepted it as gospel. And believing that, why would they care to remember the war?

Perhaps now the war’s centennial will encourage Americans to reexamine their nation’s part in the Great War. Perhaps they’ll rediscover that America’s role was, in fact, indispensable. A few of them might even choose to write about it.

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