(CNN)He stood 5-foot-4 and weighed 130 pounds. An angular, baby-smooth face made him look even less intimidating. Henry Johnson was at first just another railroad porter who toted luggage and smiled for tips.
From Syria to Black Lives Matter: 3 ways WWI still shapes America
But on May 4, 1918, Johnson grabbed a two-inch bolo knife and a splintered rifle and did something so remarkable that he earned another name: "Black Death."
Johnson was a US sergeant standing sentry one night in a French forest when a German raiding party attacked. The swarming Germans shot Johnson in his lip, head and side. Yet Johnson kept shooting back. When his rifle jammed, he grabbed it by the barrel and clubbed more Germans. Then he used the bolo knife to stab and disembowel another enemy soldier. He kept throwing grenades until he fainted from blood loss.
When his comrades found Johnson the next morning, they discovered he had killed four Germans and wounded about 20 more. They could still see the bloody trails of wounded Germans who had crawled into the woods to escape Johnson's fury. Johnson had been wounded 21 times but somehow survived the hourlong battle.
"There wasn't anything so fine about it," Johnson would say later when praised for his gallantry. "Just fought for my life. A rabbit would have done that."
Johnson's story is featured in PBS' "The Great War," a stirring account of America's entry into World War I. The three-part "American Experience" film, which begins airing Monday, devotes six hours over three nights to explaining why the nation decided to enter "the war that would end all wars" 100 years ago this month.
Johnson's story captures what's distinctive about the film. He was a black soldier who faced something even more lethal than German bayonets when he returned home. He discovered an America that was also at war with itself. Some of the most ferocious battles during World War I took place not in Europe but on the streets of America -- and some are still being fought today.
What should the President do when a foreign dictator is accused of murdering women and children? Does the US welcome too many immigrants? Are corporations too powerful? Are women treated like second-class citizens? Those might seem like questions ripped from today's headlines, yet they literally provoked riots and lynch mobs during World War I, the film shows.
Few people today, however, know how relevant the war remains because it seems so distant, trapped forever in wobbly black-and-white silent film, historians say.
"The First World War is the most important event that most people don't know about," says Dan Carlin, a historian whose "Hardcore History" podcast examines World War I. "It's a Pandora's box. We're still ironing out what it unleashed."
Here are three battles from "The Great War" the United States is still waging:
They speak in funny accents and don't care about fitting in. So many are pouring across the border that they're threatening the American way of life. They're not real Americans.
That's what many Americans thought of German-Americans during World War I.
If you think political battles over immigration are tough today, they were vicious when America entered World War I, "The Great War" shows. A wave of hysteria aimed at German-Americans swept the nation as it struggled to assimilate what was then its largest ethnic group.
America didn't just declare war on Germany -- it waged war on German-American culture. Newspapers warned of "German troublemakers" and "German traps." People refused to drink German beer, and children were instructed to rip German songs out of music books. In one Ohio town, officials slaughtered all dogs belonging to German breeds.
A German-American coal miner accused of being a spy was even attacked by a mob, stripped of his clothes and hanged from a tree, the film reveals. The Washington Post applauded the mob's actions.
"Big parts of the American public lost their minds about the nature of the society they live in and the threats they faced from their neighbors who happen to have German names," Pulitzer Prize-winning historian David Kennedy says in the film.
It was a time of demographic panic. When World War I erupted in Europe in 1914, the United States had a population of about 100 million immigrants. Millions of other Americans had parents who were born abroad.
Those citizens who didn't fit the definition of a "real American" faced persecution and torture. One of the most wrenching segments in the film looks at the story of three US citizens who became conscientious objectors to the war. They were David, Michael and Joseph Hofer, otherwise known as the "Hofer brothers."
The three South Dakota men were members of the Hutterites, a group of Christian pacifists. Hutterite men already drew suspicion because they wore long beards and hair and spoke German.
When the Hofer brothers were drafted, they refused to fight or wear a uniform. They were imprisoned in Fort Leavenworth, Kansas, and brutally treated. They were denied food and water, forced to stand in freezing temperatures with scant clothing, and chained in a cell for up to nine hours a day. Two of them died. But none recanted their religious beliefs.
"It's really torture," Michael Kazin, author of "War Against War: The American Fight for Peace, 1914-1918," tells the film. "It has to be called that."
As a final indignity, the body of one of the two brothers who died was dressed in the military uniform he refused to wear when he was alive.
Brutality wasn't confined to the trenches of Europe. There was plenty of it in the streets of America.
When President Donald Trump dispatched Tomahawk missiles to an air base in Syria last week after the country's ruler was accused of launching lethal chemical attacks, he was operating from a script first penned by President Woodrow Wilson during World War I.
It was Wilson who said America should enter the war to make the world "safe for democracy." The notion that America had a moral responsibility to respond militarily to atrocities abroad began during World War I, "The Great War" shows.
"The modern version of the United States is born in this war," says Carlin, the "Hardcore" podcast historian.
"The Great War" also shows how the idealism of war can be used to crush populist movements.
World War I occurred during a surge of progressive activism in the United States. The labor movement was powerful, and socialists, communists and anarchists were common figures in public life. Women were leading the anti-war effort as well as crusading for the right to vote.
Yet much of this progressive momentum was halted by a crushing of popular dissent by the federal government, the film shows.
During the war, Wilson signed the Espionage Act and Sedition Act, which made it illegal to say almost anything against the United States or its war effort. Criticism of the US became dangerous. American internment camps didn't begin with the Japanese in World War II. The US government created them for political prisoners during World War I, the film shows.
That suppression even targeted one of the most famous progressive leaders of the time, Eugune Debs. Debs was the Bernie Sanders of his day. A socialist labor organizer and presidential candidate, he was arrested in 1918 for giving an anti-war speech and sentenced to 10 years in prison under the Espionage Act.
Wilson ultimately paid a price for his clampdown on radical and liberal groups. After the war ended, he tried to create a League of Nations that would mediate international disputes and prevent another world war from erupting. But he couldn't get the US Senate to agree to join the League, in part because his crackdown on anti-war activity had alienated or weakened any potential progressive allies.
Wilson would die of a stroke just six years later. He is depicted in the film as a tragic figure -- idealistic but deeply racist, a gifted politician who could have seen his League of Nations succeed if he had just bent a little to his political opposition.
"There comes a time when bitterness overtakes shrewdness, and to the end of his life he was a very bitter man," Yale historian Jay Winter says of Wilson in the film. "I don't know anyone who can tell me why it was that Wilson didn't compromise. And as a result, he loses it all. He loses everything."
She was born to a prosperous Quaker family in New Jersey but spent her life reviled by much of the American public. She was attacked by angry mobs and force-fed in prison after going on a hunger strike. Once, prison officials even tried to declare her insane.
Nevertheless, Alice Paul persisted.
One of the revelations of "The Great War" is the prominence of American women in the debate about World War I. It was a time of surging women's activism that would culminate in 1920 with the ratification of the 19th Amendment, giving women the right to vote.
Paul is one of the most fascinating characters in "The Great War." She would have fit right in with the massive Women's March on Washington the day after Trump was inaugurated. She placed relentless pressure on Wilson by asking how America could fight for democracy abroad while denying women the right to vote at home.
Black American soldiers fought some of the same battles to proclaim their humanity, the film points out.
When many entered the war, they were initially kept from the fighting by being assigned to clean latrines pits and unload supplies. Some were paired with French fighting units, who treated them with more respect than their white counterparts. Some of the most moving images from the film show black soldiers smiling and bantering easily with French troops.
That experience transformed many black soldiers. Some historians even trace the beginnings of the modern-day civil rights movement to those black soldiers who returned from World War I determined to assert their rights. In the film, Adriane Lentz-Smith, a Duke University associate professor of history, describes the metamorphosis in black soldiers who served in France:
"Folks didn't think about the etiquette of white supremacy any more than a fish thinks about the wetness of water. But when you step out of a system that people have told you is the only way, and then you look around and there are these people in the world working under a different set of rules, it changes people's imagination."
White America, though, wasn't ready for this New Negro. When these black soldiers returned home, many were greeted by the "Red Summer," often described as a wave of deadly race riots that swept through at least 25 American cities in 1919.
Calling them race riots, though, doesn't fully capture what happened, says Lentz-Smith, author of "Freedom Struggles: African Americans and World War I."
"You say riots and people think breaking shop windows and stealing stuff," she says. "They don't have a sense of what white mob violence really looks like. This is going into a black community on a rampage, trying to destroy black wealth, trying to hurt or kill black people. Folks say they're more akin to pogroms in the Jewish communities than any kind of riots we're seeing now."
This is the world Sgt. Johnson returned to after his heroic exploits in France. The French army awarded him its highest medal for valor. But the US Army didn't mention his 21 wounds in his discharge papers or give him disability pay. He returned to his job as a railway porter in Albany, New York, but his injuries made it impossible to continue.
Johnson's health faded as he descended into alcoholism and poverty. His wife and children left him, and he died in 1929 at age 32. His descendants believed he was buried in a pauper's grave.
But Johnson's story still had a surprise or two left.