FILE - This undated file image shows African-American social reformer, abolitionist and writer Frederick Douglass. Douglass was the country's most famous Black man of the Civil War era, a conscience of the abolitionist movement and beyond and a popular choice for summing up American ideals, failings and challenges. (AP Photo, File)

 (CNN) — In mid-19th-century America, when public speaking was a form of mass entertainment, Frederick Douglass was a rock star.

Standing-room-only crowds greeted him in the US and in Europe. People wept as he recounted the horrors of slavery or erupted in laughter as he mimicked his former slave master. White spectators openly gushed about Douglass’ “muscular, yet lithe and graceful” 6-foot, 200-pound frame, his “full and rich” baritone, and compared him to an “African prince.”

When people talk today about Douglass’ speaking prowess, they often cite his defiant “What to the Slave is the Fourth of July?” address. But he gave another speech that deserves wider recognition because Douglass spoke with uncanny precision about the kind of debates we’re having now about race, immigration, and what makes America exceptional.

The speech is called “Composite Nation” and in it Douglass tackles a question that lurks behind many of the current political debates in the US: Is the country better off having a multitude of races, ethnic groups and religious beliefs? Or would it, and other nations, fare better with a homogenous population where most people look alike and share the same religious beliefs?

Douglass’ answer has inspired and challenged historians for over a century. The historian Jill Lepore called it “one of the most important and least-read speeches in American political history.” And the historian Andrew Roth said Douglass’ address is “one of the earliest and still most eloquent” tributes to the beauty of America’s ever-expanding definition of the “We” in “We the people.”

“The Composite Nation speech is a brilliant vision of America’s evolving “tapestry” in all its colors, shades, and ethnicities,” Roth, a scholar-in residence at the Jefferson Educational Society, wrote.

Douglass’ bold vision of America takes on fresh relevance today as PBS premieres a new documentary about his life by Oscar-nominated filmmaker Stanley Nelson. Entitled “Becoming Frederick Douglass,” the film looks at how a man born into slavery became one of the nation’s most influential leaders. Douglass was the most photographed American of the 19th century (160 photographs of him survive, compared to 130 of Abraham Lincoln).

The documentary is filled with memorable moments. Narrated by actor Wendell Pierce, it retraces many pivotal moments in Douglass’ life: How he traded biscuits as a boy with White playmates to learn how to read; the crucial contributions of his first wife; his legendary two-hour fight with an overseer; and a recreation of his famed Fourth of July speech.

The film suggests that Douglass’ facility with words was just as important as his physical courage in taking on the institution of slavery.

“When you read something like the Fourth of July speech, you get the sense that Douglass saw words as battle axes,” says Derrick. R. Spires, a Cornell University professor who appears in the film.

Yet to freeze-frame Douglass’ life in the familiar contours of 19th-century American history misses out on the radical nature of his “Composite Nation” (also known as “Our Composite Nationality”) speech.

What makes it great? And why is it so little-known today?

The audacious optimism at the heart of Douglass’ speech

Part of its greatness is due to timing. Douglass was sketching a vision of a post-racial America a century before the term was invented.

He delivered the first version of the speech in 1869 in Boston. A bloody Civil War fought over slavery had ended only four years earlier. The country was attempting to build its first multiracial democracy through the passage of the 13th, 14th and 15th Amendments, which ended slavery, granted Black men the right to vote and introduced birthright citizenship.

But overt White supremacy was still a social and political norm. Many White Americans believed Black people were genetically inferior. Anti-Irish and German-Catholic prejudice was pervasive. Chinese immigrants were being attacked and lynched by mobs, and by 1882 the US Congress would pass the Chinese Exclusion Act, the first significant law restricting immigration in the US.

It was a time in America when people openly embraced Social Darwinism, the idea that White people were meant to rule over others because they were innately superior. That belief was so ingrained that a politician like Garrett Davis, a Democratic senator from Kentucky, could openly say:

“I want no Negro government; I want no Mongolian government; I want the government of the White man which our fathers incorporated.”

But Douglass’ Composite Nation speech was filled with an audacious hope that belied the pervasive prejudice of his era. He said he supported Chinese immigration to America and hoped for the day when more Chinese people could become citizens, vote and hold office.

“I want a home here not only for the Negro, the mulatto and the Latin races; but I want the Asiatic to find home here in the United States, and feel at home here, both for his sake and for ours,” Douglass said.

He also argued that immigration made the US stronger and scorned those who believed White people are the “owners of this continent” and that “it is best not to take on board more passengers than the ship will carry.”

His pointed to other isolated countries of his era whose leaders boosted of their “pure blood” but lagged behind all other countries in dynamism and prosperity.

“Those races of men which have maintained the most separate and distinct existence for the longest periods of time; which have had the least intercourse with other races of men, are standing confirmation of the folly of isolation,” he said.

The glue holding together this Composite Nation would be the “principle of absolute equality,” he said, no matter one’s race, ethnicity or religious beliefs.

“We shall spread the network of our science and civilization over all who seek their shelter, whether from Asia, Africa or the isles of the sea,” he said. “We shall mold them all, each after his kind, into Americans…”

Why Douglass’ speech was so radical

No political figure — not even Abraham Lincoln — talked that way about the US in the mid to late 19th century. Lincoln once proposed to end slavery by shipping willing slaves back to Africa, and said that he could not envision Black and White people living together in social and political equality.

Nicholas Bromell, a historian who appears in the PBS film, says it was routine for even progressive leaders like abolitionists to warn of the “hordes” of Chinese immigrants coming to America during that era.

“He was way ahead of his time,” says Bromell, author of “The Powers of Dignity: The Black Political Philosophy of Frederick Douglass.”

“He was speaking for a multiracial, diverse America in the 1860s,” he says. “He was absolutely alone. I can’t think of another public figure who took such an unequivocal position like he did.”

Some 150 years later, Douglass’ vision of the US as a “multi-hued global beacon of liberty” remains fiercely contested.

Many contemporary Americans seem pessimistic about the prospect of building a modern-day Composite Nation — a multiracial, multiethnic and multireligious democracy that reflects the changing demographics of the country.

The signs that people and politicians are losing faith in American democracy are everywhere.

One recent poll found that 64% of Americans believe that their democracy is “in crisis and at risk of failing.”

Conservative American politicians have expressed open admiration for leaders such as Hungarian Prime Minister Viktor Orban, who is widely seen as eroding democracy in his country in part by demonizing immigrants and eroding democratic norms.

Republican Party leaders now describe the Jan. 6 insurrection at the US Capitol as “legitimate political discourse.”

Posts and searches for the term “civil war” have recently spiked on social media and podcasts as the midterm elections approach.

And a White Christian nationalist movement, which insists that America was created to be a White, Christian nation, is growing in power.

Former President Ronald Reagan, once the face of the GOP, described the US in his 1989 farewell address as a nation “teeming with people of all kinds living in harmony and peace,” with doors “open to anyone with the will and heart to get here.”

But Donald Trump, the leader of today’s GOP, has long expressed hostility to non-White immigrants coming to the US from “s***hole countries.

History has validated many of Douglass’ claims

Douglass confronted an even more hostile political climate than democracy advocates face today.

In his Composite Nation speech, he took on critics who couldn’t imagine that a multi-racial democracy could work. He called them “ministers of despair” and mocked critiques such as “You will never make the Negro work without a master, or make him an intelligent voter, or a good and useful citizen.”

He implied that constant predictions of democratic doom could become self-fulfilling prophecies. Keep listening to people who say democracy can’t work, and it won’t.

“They never see the bright side of anything and probably never will,” Douglass said of these critics. “Like the raven in the lines of Edgar A. Poe they have learned two words, and these are ‘never more.'”

Many of Douglass’ claims have been validated by the passage of time.

Consider the impact of immigrants. Many immigrants today outwork, outvote and outfight native-born Americans — as Douglass predicted they would a century and a half ago. One in five Medal of Honor recipients have been immigrants. Immigrants are nearly twice as likely to start businesses as native-born Americans. And nearly half of all Fortune 500 companies — including Apple, Google and Amazon — were founded by immigrants and their children.

Diversity has other strengths as well. Groups that include people with different backgrounds and cultures consistently come up with more innovative solutions to problems because they’re not confined to one perspective, research says.

Douglass was also ahead of his time in rejecting the notion of inherent differences between races. Science has since confirmed that race is a biological fiction — there is only one human race, homo sapiens.

“Man is man, the world over,” Douglass said in his speech. “A smile or a tear has no nationality; joy and sorrow speak alike to all nations, and they, above all the confusion of tongues, proclaim the brotherhood of man.”

Douglass’ optimism may sound quaint today. And there is undeniably a part of White America that has long been suspicious of democracy.

Some Founding Fathers opposed granting the vote to ordinary citizens, and early electoral districts were kept large to inhibit campaigning by all except those wealthy enough to travel across their expansive boundaries, the historian Lawrence Goldstone wrote in a recent essay called “America, then and now.”

Many didn’t think ordinary citizens could be entrusted to lead their own government, and that only those who owned real property should be allowed to vote.

For that reason, only 6% of the nation was eligible to vote in the first presidential election, Goldstone said.

But he said that what makes the US the envy of the world is its citizens’ halting yet ultimately successful struggle to expand the very rights the Founders sought to limit.

“People from virtually every country in the world wanted to come to the nation that Americans struggled for decades and decades to create, as imperfect as it remains,” he wrote. “They did not come because its leaders disparaged the poor, incarcerated racial or political minorities, or mocked the handicapped and those whose sexual orientation did not fit in faux religious boxes. If that is what they wanted, they had any number of other choices, such as Iran, Russia or Hungary.”

Why Douglass’ speech never caught on

Douglass lived until 1895, long enough to see much of the promise of his Composite Nation tarnished. He saw the Supreme Court demolish hard-won laws that granted Black citizens political power. He saw the rise of Jim Crow and murderous White mobs that used insurrectionist violence to attack and overthrow biracial governments throughout the Deep South.

The vision he had of America was “in tatters,” the historian David Blight, who won the Pulitzer Prize for “Frederick Douglass: Prophet of Freedom,” said in an essay.

“By the 1890s Douglass, aging and in ill health but still out on the lecture circuit, felt hard-pressed to sustain hope for the transformations at the heart of the “Composite Nationality” speech.”

As time passed, his Composite Nation optimism may have seemed increasingly out of touch. People likely related more to the fury Douglass expressed at American hypocrisy and racism in his 1852 Fourth of July speech.

“As nativism, racism, and nationalism converged in the closing decades of the 19th century, the idea of America as a cosmopolitan nation of immigrants fought for survival,” Blight wrote.

A battle is still being fought over that idea today.

Douglass’ vision of America as a multi-hued beacon of global liberty still looms ahead of us like a rhetorical North Star. It might seem far-fetched, but we’ve already seen the alternatives — in the January 6 insurrection and the mounting sense of dread many Americans now feel about the future.

Douglass lived in an even more brutal era and experienced the worst forms of racial prejudice and American hypocrisy.

And yet he still believed that we could, and would, do better. So should we.