The owners of a farm in northern France return to their land, devastated by the war, in 1919.ADOC/Corbis

The First World War, George Kennan wrote decades after it ended, was the ur‑catastrophe of the 20th century. The first conflict among industrialized global powers killed 10 million soldiers and mutilated over 21 million more.

Both the war and the peace that followed have marked our world in indelible ways. Especially Europe. The deaths of more than 110,000 Americans in uniform, half to the Spanish flu, were equivalent to just one-quarter of the death toll in the French army alone during the first four months of the war. Europe suffered a bloodbath such as the world had never seen. Two million German soldiers died, along with about 1 million British troops, counting those from the colonies and dominions. Proportionately higher losses were suffered in Russia, Serbia, and Ottoman Turkey, where a war of 20th-century firepower was fought under 19th-century sanitary conditions.

The contrast between American and European perceptions of the world order in the 20th and 21st centuries is incomprehensible without considering the catastrophe of 1914–18. Ever since, Europe has felt an underlying pessimism, a sense of danger and disorder that the United States hasn’t shared. Americans have continued to believe that progress is built into history. Most Europeans, other than Marxists, dropped this notion once the Great War began.

Europeans still call it the Great War—not only because it was huge and momentous, but also because it changed the nature of war itself.

How so? First, by obliterating the distinction between civilian and military targets. After the early battles of 1914 resulted in a bloody stalemate, the conditions of civilian life behind the lines of occupying armies deteriorated. The Great War created internment camps all over Europe and beyond, to house enemy aliens in the wrong country at the wrong time. Still worse was the treatment of ethnic minorities suspected of disloyalty. After a series of defeats in 1915, the Russian army sent hundreds of thousands of Jews in Galicia from the battlefront to the interior, in case they might welcome German invaders. Armenians in Turkey fared still worse; more than 1 million died in the 20th century’s first European genocide.

The bombardment of cities by artillery and aircraft also brought the war to civilians. The German naval warfare against civilian shipping ultimately drew the United States into the war. The Allied blockade of European ports, which continued after the armistice in 1918, was a clear violation of international law.

And consider the changes in mood the war wrought in the United States. The 20 years before the war had seen waves of immigrants arrive from central and eastern Europe, inspiring the use of an epithet—“hyphenated Americans”—that intensified in the course of the war. The loyalties of German Americans, in particular, were thrown into question. The intolerance of wartime continued and grew more vitriolic once a prosperous peace returned. Government witch hunts conducted after the war, such as the so‑called Palmer raids against suspected radicals and anarchists, many of them foreign-born, had their origins in the war itself.

Nine months after the war broke out, the fighting turned even uglier. In April 1915, modern chemical warfare was born on the battlefields of Belgium, and soon became a tolerated (although never legalized) form of weaponry used by all combatants on a frightening scale. In 1918, one of every four shells fired on the western front contained poison gas.

The clouds of chlorine, then phosgene, then mustard gas did not bring any tactical or strategic breakthrough. For one thing, their effectiveness depended on the wind’s direction and the absence of precipitation. When it rained, as it did frequently in Flanders, the gas never rose above ankle level, meaning a soldier could survive if he stayed on his feet. But gas warfare changed the rules of engagement. Gas masks were rudimentary, and left men (and animals) in no-man’s-land without adequate protection. Gas didn’t change the balance of power, but it did change the balance of horror that soldiers faced on the battlefield.

Later, poison gas was used outside Europe—allegedly in Iraq as early as the 1920s, then in Manchuria and Ethiopia in the 1930s. Fear of retaliation, stemming from military leaders’ firsthand experience of gas as soldiers themselves during the Great War, apparently deterred its use against soldiers in World War II, although the Nazis employed Zyklon B, previously known as a powerful pesticide, in concentration camps.

Might gas warfare have come into widespread use without the Great War? Perhaps, but the huge investment in weapons of mass destruction in 1914–18 left a precedent that could not be eradicated. The use of poison gas is with us still, notably in Syria.

The peace treaties signed at the end of the war left a damaged world with an impossible legacy: they handed over control of German colonies in Africa and the Pacific to the victorious powers and inspired hope around the world that Woodrow Wilson’s notion of self-determination for subject peoples would lead to the end of empires. Not quite. Self-determination was the property of the former nations, such as Czechoslovakia, Hungary, Poland, and Serbia—all predominantly Caucasian—embedded in the German, Austro-Hungarian, Ottoman Turkish, and Russian empires. Populations of color would have to wait until, under the mandate of the imperial powers, they reached the “maturity” needed for self-government. When would that be? Nobody could say.

Besides, no matter what was decided during the postwar peace conference at Versailles, the imperial powers had already made their own plans for the Middle East. In 1915, the British high commissioner in Egypt promised the keeper of the holy sites in Mecca independence for Arabs in return for their participation in fighting the Ottoman empire. Two years later, Britain’s Balfour Declaration promised Zionists the opposite: a Jewish homeland in Palestine. And these incompatible promises were complicated even more by the secret Sykes-Picot Agreement in 1916, which divided the post-Ottoman Middle East between French and British spheres of influence and drew arbitrary borders—in Iraq, for instance—that have caused instability and conflict ever since.

As a result, violence exploded outside of Europe in 1919–21, when people who had served the Allied cause militarily and otherwise discovered that their recompense would be pious words and nothing more. This happened first in Egypt, then India, then Korea, then China. The wartime collapse of the Ottoman empire brought down its sultan, the all-powerful caliph, and created a crisis in Islam, which lost its spiritual center; Muslim-dominated countries remained colonies ruled (often poorly) by imperial powers under the aegis of the League of Nations. The Muslim Brotherhood, founded in Egypt in 1928 to counter Western exploitation of the Islamic world, was the precursor to al-Qaeda.

The Great War cast its geopolitical shadow across the Far East as well. The extent to which the war fueled the continuing hostility between China and Japan is rarely recognized. The problem arose from the Treaty of Versailles. Both nations, traditionally rivals, were among the victorious delegations. China, however, was the weaker power, plagued by internal strife after its 1911 revolution. Japan had helped the Allies during the war, by convoying Australia’s and New Zealand’s troops across the Indian Ocean and by sending naval cruisers to protect the west coast of Canada. At Versailles, Japan tried to exploit its newly acquired leverage, proposing that the charter of the League of Nations include a commitment to racial equality. President Wilson, as a southern-born politician, knew that any such language would ensure the treaty’s defeat in the U.S. Senate. To prevent the Japanese from walking out of the peace negotiations once their request was turned down, the leaders of Britain, France, and the United States backed Japan’s proposal to grant it temporary control—until 1922, as it turned out—of the Chinese province of Shandong, south of Beijing, which the Germans had controlled during the war.

So much for the principle of self-determination. When push came to shove, Wilson chose to reward Japanese naval power and ignore political justice. When Wellington Koo, a Chinese delegate in Paris, sent home the decision on Shandong, students in Beijing responded with shock and outrage, quickly calling for a mass demonstration at Tiananmen Gate to protest the treaty. At a rally the next day, they formed a new organization called the May Fourth Movement, out of which emerged China’s Communist Party. Ponder this: Woodrow Wilson was its godfather.

Next year, China will host the 22nd Congress of the International Committee of Historical Sciences. Where? In the city of Jinan, the provincial capital of Shandong, a choice likely intended to remind historians that both Japan and the West have a history of humiliating China. Those days are over, but the memories linger.

Beyond the advances in the science of murder and the geopolitical reworkings, the Great War created a deep shift in the public attitude toward war itself. The Great War discredited the concept of glory, a word that many Europeans simply could not swallow. The British poet Wilfred Owen, killed late in the war, wrote that anyone who witnessed a soldier suffocating slowly from poison gas would never repeat “to children ardent for some desperate glory / the old Lie” that it was noble to die for one’s country.

The “old Lie” had been told time and again in the popular press and public rhetoric. The use of literature and painting in the service of war was mocked mercilessly in the nonsense verse of the Dada movement and in the nightmare paintings of the surrealists. To clean away the damage that propaganda had done to the literary arts—and indeed to language itself—radical steps were necessary. No longer could dismembered or mangled corpses be sanitized as “the fallen,” nor the butchery of the trenches portrayed as heroic. Artists throughout Europe denounced the obscenities of a war fought for what the poet Ezra Pound called a “botched civilization.” The millions of men slaughtered deserved more than elevated prose; they deserved the unadulterated truth.

At the same time, the arts saw a counterrevolution, a movement back in time that highlighted the power of classical, religious, and romantic forms to memorialize the dead. Modernism excited, shocked, and stimulated, but it did not help people mourn. For that, a bereaved generation turned to the classical art of Edwin Lutyens’s cenotaph in London, the religious art of Rouault, and the sculptures and lithographs of mothers mourning their dead sons created by the German artist Käthe Kollwitz, whose own son had been killed in Belgium in 1914.

After the war, a generation of soldiers wrote their memoirs, which sold by the millions. The story they told was binary—the jarring contrast between innocence and experience, between hope and disillusionment. It depicted the unimaginable awfulness of the war, during which the millions of men in the trenches entered a world as inhospitable and desolate as the dark side of the moon. There they encountered artillery fire—the great killer of the Great War—on a scale the world had never seen before.

As a consequence, 5 million of the men who died in the war have no known graves. The stalemated war on the western front meant that unceasing bombardments pulverized the corpses buried in makeshift cemeteries. On the eastern front, the war was so fluid and covered such distances that finding bodies, let alone identifying and burying them, wasn’t possible. In effect, war had been transformed from a killing machine into a vanishing act.

For fully half the men who were killed in the war, nothing was left but their names. That, and the scarier, shakier, more intolerant world that the war to end all wars created.

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