Four years ago, I went to war. Like many of the people whose stories I followed in my daily “live-tweets” on World War I, I had no idea what I was getting myself into. What began as an impulsive decision to commemorate the hundredth anniversary of Austrian Archduke Ferdinand’s death at the hands of a Serbian assassin, in June 1914, snowballed into a blood-soaked odyssey that took me—figuratively and literally—from the rolling hills of northern France, to the desert wastes of Arabia, to the rocky crags of the Italian Alps, to the steel turret of a rebel cruiser moored within range of the czar’s Winter Palace in St. Petersburg, Russia. And like the men and women who actually lived through it, now that the Great War is ending I find myself asking what, if anything, I’ve learned from it all.

In the American mind, World War I typically occupies an unimpressive place as a kind of shambolic preamble to the great good-versus-evil crusade of World War II, a pointless slugfest in muddy trenches for no worthy purpose, and no worthwhile result. Its catchphrases—“The War to End All Wars,” “Make the World Safe for Democracy”—evoke a wry and knowing chuckle. As if. But the war I encountered, as it unfolded day by day, was far more relevant, passionate, and unpredictable.

Posting daily newspaper clippings and photographs, found mainly in books and online archives, I began to see the Great War as a kind of portal between an older, more distant world—of kings with handlebar mustaches, splendid uniforms, and cavalry charges—and the one that we know: of planes and tanks, mass political movements, and camouflage. It snuffed out ancient monarchies in czarist Russia, Habsburg Austria, and Ottoman Turkey, and gave birth to a host of new nations—Poland, Hungary, Czechoslovakia, Syria, Iraq, Jordan, Lebanon, Finland, Estonia, Latvia, Lithuania, Ukraine, Armenia, Azerbaijan—that, in their struggles to survive and carve out an identity, continue to shape our world today. The British declared their intent to create a national homeland in Palestine for the Jews.

The needs of the war brought women into the workforce, and helped win them the right to vote. The huge privations it inflicted triggered the world’s first (successful) Communist revolution, and the frustrations it unleashed prompted many, afterward, to turn to far-right authoritarians in Italy and then Germany. And finally—though many have forgotten it—the comings and goings of people caused by the war helped spread the deadliest epidemic the world has ever known: the 1918 influenza virus, which quietly killed an estimated 50–100 million human beings in their homes and in hospitals, more than both world wars combined.

I also encountered a cast of characters more varied and amazing than I thought possible. Rasputin, the dissolute Russian mystic who warned Czar Nicholas that going to war would destroy his dynasty, and was murdered in part because he was (falsely) suspected as a German agent. The Austrian Emperor Karl, who inherited a war he didn’t want, and tried fruitlessly to make peace. T.E. Lawrence, a scholarly young intelligence officer whose affinity for the Arabs helped turn them to the Allied cause, and shaped the modern Middle East. Mata Hari, a Dutch-born exotic dancer who played double-agent, seducing high-ranking Allied and German officers for valuable information, until she was caught and shot by the French as a spy.

Some of the names are familiar, and offer hints of future greatness—or infamy. A young anti-war journalist named Benito Mussolini, sensing the way the wind blows, changes his tune and aggressively advocates for Italy to enter the war, before signing up himself. A young Charles De Gaulle is wounded at Verdun and taken prisoner for the rest of the conflict. A relatively young Winston Churchill plans the disastrous Gallipoli Campaign and pays his penance by serving in the trenches, before making a political comeback. A young Harry S. Truman serves as an artillery officer on the Western Front, alongside (and outranked by) a young George C. Marshall (his future Army Chief of Staff and Secretary of State) and Douglas MacArthur (his future general in the Pacific and Korea). A young George S. Patton develops a fascination with tanks. A young Walt Disney doodles cartoons on the side of the ambulances he drives, in the same unit as a young Ray Kroc (the founder of McDonald’s). Another young ambulance driver, Ernest Hemingway, finds inspiration on the Italian Front for his novel A Farewell to Arms. A young Hermann Göring (later head of the Luftwaffe) becomes a dashing flying ace, while a young Erwin Rommel wins renown fighting at Verdun and in the Alps. Meanwhile, an odd young German corporal, who volunteered in the very first days of the war, is blinded by poison gas in its final days, and wakes up in hospital to the bitter news that Germany has lost. His name is Adolf Hitler.

The dramatic panoply of people, places, and events, however, only occasionally rises to the fore. For the most part, the war is a steady stream of ordinary people doing ordinary things: washing their clothes, attending a concert, tallying supplies, fixing a car. History books give us a distorted sense of time, because they fast forward to major events. A day may take a chapter, a month may be passed over in a sentence. In fact, there were periods where nothing much happened—plans were being made, troops trained, supplies positioned—and when you live-tweet, you experience that waiting. Sometimes, it led to intriguing surprises, like photographs of dragon dances performed by some of the 140,000 Chinese laborers brought over to France to lend muscle to the Allied war effort. Mostly, it was a matter of endurance. Each winter, the fighting came to almost a complete stop as each country hunkered down and hoped its food would last. The “turnip winter” of 1916–1917, when the potato crop failed, nearly broke Germany; the increasingly desperate craving for “bread and peace” did break Russia the following year.

The future president Herbert Hoover made his reputation by coordinating food relief shipments to German-occupied Belgium, and later as the US “food czar” ensuring Allied armies and populations were fed. The vast mobilization was effective: by 1918, the Allies were able to relax their food rationing, while Germany and its confederates, strangled by an Allied naval blockade, were on the verge of starvation. America’s war effort was accompanied by a vast expansion in the federal government’s power and reach. It nationalized (temporarily) the railroads and the telephone lines. It set prices for everything from sugar to shoes, and told motorists when they could drive, workers when they could strike, and restaurants what they could put on their menus. It seized half a billion dollars of enemy-owned property, including the brand rights to Bayer aspirin, and sold them at auction. The US government also passed espionage and sedition laws that made it illegal to criticize the war effort or the president. Some people were sent to prison for doing so, including the Socialist Party leader Eugene V. Debs, who ran for president for a fifth and final time from a cell.

Winning the war, however, was far from a sure thing. For three years, the Allies threw themselves against an evenly-matched enemy on the Western Front, without making any breakthroughs, while the Eastern Front gradually crumbled. An early Allied foray to take out Turkey, at Gallipoli in 1915, ended in bloody disappointment. Inducing Italy to enter the war on the Allies’ side, that same year, was supposed to swing the entire conflict in their favor; instead, the catastrophic Italian rout at Caporetto, in the autumn of 1917, put the Allied effort in greater jeopardy. When Lenin seized power in Russia, at the end of 1917, he took it immediately out of the war and ceded immense land and resources to German control. True, the US had by then entered the war, in response to Germany’s submarine campaign against merchant ships and its clumsy diplomatic scheming in Mexico. But with the war in the East essentially won, the Germans saw a window in which they could shift all of their armies to the West and crush the exhausted British and French before enough American troops could arrive to make a difference. Their spring offensive, or “Kaiser’s Battle,” in early 1918 drove deep into Allied lines, prompting the French government to evacuate Paris.

The Germans’ big roll of the dice failed. The Allies held, and the US mobilized much faster than anyone expected. By the summer of 1918, a perceptible change had taken place. Hundreds of thousands of American troops were arriving every month at French ports, and their first units were taking part in battles, piecemeal at first, to push the Germans back. Even in September, however, nearly everyone expected the war to continue into 1919. That was when a huge US army of 3 million men would be ready to take part in a big Allied offensive that would drive all the way to Berlin. It never happened. That fall, the German army—and those of Turkey, Austria, and Bulgaria—first buckled, then collapsed like a rotten log. By November 11, the war was over.

The fact that nobody saw the end coming, the way it did, highlights the value of going back, a hundred years later, and reliving events day by day, as they took place. What may seem obvious now was anything but so then, and we do the people who lived through it, and our understanding of them, a real disservice when we assume that it was. “Life can only be understood backwards,” the Danish philosopher Søren Kierkegaard observed, “but it must be lived forwards.” The British historian C.V. Wedgewood elaborated on the same idea: “History is lived forwards but is written in retrospect. We know the end before we consider the beginning and we can never wholly recapture what it was like to know the beginning only.” We can’t entirely forget that we know what happened next, but when we at least try to identify with people who did not know, we shed new light on them, and on what did happen.

Take the Russian Revolution. We see it as the birth of a Communist superpower, and struggle to make sense of the seemingly half-baked, half-hearted effort by the Allies to intervene by sending troops, including Americans, to Russia’s ports in the far north and far east. People at the time, however, saw it almost entirely through the prism of the Great War. At first, the Allies welcomed the overthrow of the czar, and believed it would rejuvenate the failing Russian war effort. By replacing an infamous autocrat on the Allied roster with a fledgling democracy, it made “making the world safe for democracy” a more credible call to arms, and helped pave the way for the US to enter the war. When Lenin took over and made a ruinous peace with the Central Powers, he was seen as simply a German puppet. And when Bolshevik forces, augmented with released German and Austrian prisoners of war, attacked a unit of Czech soldiers crossing Siberia to rejoin the Allies on the Western Front, those suspicions blossomed into fear of a full-fledged German takeover of Russia. The Allies sent troops to key Russian ports to secure the war supplies stockpiled there and provide an exit route for the loyal Czechs. They considered trying to “reopen” the Eastern Front, but realized it would take far too many men. They assumed that when Germany was defeated, their proxy Lenin would eventually fall, and when the war ended, they naturally lost interest. It all makes sense, but only if you see through the eyes that people saw through at the time.

Did it really matter who won the war? In its aftermath, the Great War came to be seen as a colossal waste, a testament to the vanity of nations, of pompous older men sending foolish younger men into the meat-grinder for no good reason. War poems like “Dulce et decorum est” and novels like All Quiet on the Western Front have crystalized this impression. But this was not how people felt at the time. German atrocities in Belgium and on the high seas—some exaggerated, but others quite real—convinced many people that civilization, as they knew it, really was at stake. I was consistently and often surprisingly struck by the sincerity of support, not just on the home front, but among soldiers who had seen the worst of combat, for pursuing the war unto victory. The tone matures, but remains vibrant: these were, for the most part, people who believed in what they were fighting for. At what point the bitter cynicism set in, after the war ended, I cannot say. But at some point, that enthusiasm, and even the memory of it, became buried with the dead.

Though, in fact, in many places the war did not actually end. An armistice was declared on the Western Front, and the armies there were disbanded and sent home. But Germany, Austria, and Hungary all descended into revolution and civil war for a time, with gangs of demobilized soldiers fighting on all sides. In Russia, the Soviet regime and its multiple enemies would battle for several years, while trying to reconquer territory surrendered when it quit the war against Germany. The Greeks tried to reclaim Constantinople from the Turks, and would be massacred when the Turks succeeded in reconsolidating their country. The Poles fought wars with the Ukrainians and the Soviets to define the boundaries of their newly independent country. Jews and Arabs continue to fight over the new lands liberated from the Ottoman Empire to this day.

In the Great War itself, over 16 million people died, including almost 7 million civilians. The US got off relatively lightly, with 117,465 people killed, just 0.13 percent of its population. In Serbia, somewhere between 17 percent and 28 percent of the country’s population was killed. But even numbers like these leave little concrete impression on our minds. Some of the most touching parts of my experience live-tweeting were the times when people would tweet back to me about a grandfather or great-uncle who fought and died in the war, and is forever twenty-four-years old in some field in France, or Turkey, or Italy, or at sea. For most people, that absence is what defined the war: someone left and never came home. The world that they shaped, by their presence and their absence, is the one that we live in, whether we realize it or not. And we, like them, can only grope our way forward, day by day, into an unknown future.