Between the Great Lisbon Earthquake and the revolutionary year of 1848 the European chattering classes had three big ideas. One was very, very good. The other two were very, very bad. We're still paying.

The good one, flowing from the pens of such members of the clerisy as Voltaire, Thomas Paine, Mary Wollstonecraft, and above all the Blessed Adam Smith, is what Smith described in 1776 as the shocking idea of "allowing every man [or woman, dear] to pursue his own interest in his own way, upon the liberal plan of equality, liberty, and justice."

Admittedly, true liberalism took a long time. "All men are created equal" was penned by a man who kept in slavery most of his own children by Sally Hemings, not to mention Sally herself. Even his co-author Ben Franklin once owned slaves. In 1775, the English literary man Samuel Johnson had ample reason to launch a sneer from London, "How is it that we hear the loudest yelps for liberty among the drivers of negroes?"

But those liberal yelps re-echoed, and had force, amplified by the repeated embarrassment over two centuries of denying slaves, apprentices, women, immigrants, anarchists, socialists, communists, Okies, Nisei, blacks, Chicanos, gays, Vietnam protesters, criminal suspects, handicapped people, gender crossers, ex-cons, drug users, smokers, and citizens of the District of Columbia their own equality, liberty, and justice.

The fruits of the new liberalism, when it could make its way against the two bad ideas (wait for it), were stunning. Liberalism, uniquely in history, made masses of ordinary people bold, bold to try out their ideas for how to improve the world by testing them in the marketplace. Look around at the hundreds of betterments that resulted: from stock markets to ball bearings, from penicillin to plate glass.

The boldness of commoners pursuing their own interests resulted in a Great Enrichment—a rise in Europe and the Anglosphere of real, inflation-corrected incomes per head, from 1800 to the present, by a factor, conservatively measured, of about 30. That is, class, about 3,000 percent. The glory of Greece and the grandeur of Rome, Song China, and the Mughal Empire might have managed a 100 percent increase over a century or so, to something like $6 a day—but eventually they all fell back to the $3 a day typical since our species lived in caves.

And now, despite the best efforts of governments and international agencies to bungle the job, liberalism is spreading to the world, from Hong Kong to Botswana.

It's astonishingly good for the poor. Add up the fruits of illiberal government action—redistribution, licensing, tariffs, zoning, building permits, farm subsidies, restrictions on immigration, foreign aid, industrial policy, a third to half of income seized as taxes by the state—and all together, they might, if you suspend your economic disbelief, raise the income of the poorest folk by, say, 30 percent, one time only. Not the 3,000 percent attributable to liberalism, which continues to grow with no end in sight.

The two bad ideas of 1755–1848 were nationalism and socialism. If you like them, perhaps you will enjoy their combination, introduced in 1922 and still for sale in Europe and implied by Donald Trump's popularity: national socialism.

Nationalism, when first theorized in the early 19th century, was entwined with the Romantic movement, though of course in England it was already hundreds of years old. It inspired reactive nationalisms in France, Scotland, and eventually Ireland. In Italy, in the form of campanilismo, or pride in your city, it was older still. (Italians will reply when asked where they are from, even if speaking to foreigners, "Florence" or "Rome" or at the most "Sicily." Never "Italy.")

What is bad about nationalism, aside from its intrinsic collective coercion, is that it inspires conflict. The 800 U.S. military bases around the world keep the peace by waging endless war, bombing civilians to protect Americans from non-threats on the other side of the world. In July 2016, we of the Anglosphere "celebrated," if that is quite the word, the centenary of the Battle of the Somme, a fruit of nationalism, which by its conclusion three and a half months later had cost the Allies and the Central Powers combined over a million casualties, most of them dismembered by artillery. Thank you for your service.

The other bad idea of the era was socialism, which can also be linked to Romanticism, and to a secularized Christianity, with its Sermon-on-the-Mount charity and an apocalyptic view of history. It's all of a piece—from central planning in Venezuela to building permits in Chicago. A communist is a socialist in a hurry and a socialist is a regulator in a hurry and a regulator is a corrupt politician in a hurry.

What's bad about socialism, aside from its own intrinsic collective coercion, is that it leads to poverty. Even in its purest forms—within the confines of a sweet family, say—it kills initiative and encourages free riding. St. Paul, not famous for being a liberal, scolded the Thessalonians: "We gave this order: 'If anyone doesn't want to work, he shouldn't eat.' We hear that some of you are living in idleness. You are not busy working—you are busy interfering in other people's lives!" Good for St. Paul.

The not-so-sweet forms of socialism, especially those paired with nationalism, are a lot worse. Thus North Korea, Cuba, and other workers' paradises. As the joke goes, "Under capitalism man exploits man; under socialism it's the other way around."

What to do? Revive liberalism, as the astonishing successes of China and India have. Take back the word from our friends on the American left. They can keep progressive, if they don't mind being associated with the Progressive movement of the early 20th century, and its eugenic enthusiasms for forced sterilization and for using the minimum wage to drive immigrants, blacks, and women out of the labor force. And we should persuade our friends on the right to stop using the l word to attack people who do not belong to the country club.

Read Adam Smith, slowly—not just the prudential Wealth of Nations, but its temperate sister The Theory of Moral Sentiments. And return in spirit to the dawn of 1776, when the radical idea was not nationalism or socialism or national socialism, but "the obvious and simple system of natural liberty" that allows all men and women to pursue their interests in their own ways.

It was a strange but very, very good idea. Still is.