President Trump has peppered his first months in office with periodic announcements about the history of the nation he now leads, which he shares in the apparent presumption that others will be similarly amazed and astonished. In February, he marked Black History Month with a rambling speech, name-checking a variety of historical figures. “I am very proud now that we have a museum, National Mall, where people can learn about Reverend King, so many other things,” he said. “Frederick Douglass is an example of somebody who's done an amazing job that is being recognized more and more, I notice.”

“Great president,” he told the congressional campaign committee of the Party of Lincoln back in March. “Most people don’t even know he was a Republican, right? Does anyone know?”

But more striking than these episodes in the education of Donald Trump are the lessons he chooses to draw from these snippets of the past. On Monday, he was speaking to SiriusXM’s Salena Zito about his admiration for Andrew Jackson, a favorite theme of Steve Bannon’s, and veered dramatically off course:

I mean had Andrew Jackson been a little later you wouldn’t have had the Civil War. He was a very tough person, but he had a big heart. He was really angry that he saw what was happening with regard to the Civil War, he said, “There’s no reason for this.” People don’t realize, you know, the Civil War, if you think about it, why? People don’t ask that question, but why was there a Civil War? Why could that one not have been worked out?

There is, as my colleague David Graham has noted, a tremendous amount to unpack in those short few lines. Most charitably, Trump may have been contrasting Jackson’s successful resolution of the Nullification Crisis in 1832 with President Buchanan’s fecklessness a few decades later, making the case that a strong leader could have imposed a deal that would have averted the war.

Jackson was prepared to use force, militia drilled in South Carolina, but a compromise averted the crisis. “We want no war, above all, no civil war, no family strife,” Henry Clay said in 1832, defending that compromise on the Senate floor. “We want to see no sacked cities, no desolated fields, no smoking ruins, no streams of American blood shed by American arms!”

But if Clay and Jackson averted war, their continuance was purchased in the blood and pain of others. There were 2 million slaves in 1830; by the time the Civil War came, there were more than 4 million held in bondage.   

The question Trump says that “people don’t ask” may be the most debated historical question in America. Union veterans of the war tended to stress the moral imperative of their cause. But by the 1890s, historians like James Ford Rhodes were starting to understand the conflict as the inevitable clash of a slave system with an industrializing economy, with slavery less a moral cause than a tectonic force impelling the conflict forward. Charles and Mary Beard, in the 1920s, deemphasized slavery in favor of class conflict between the agrarian South and industrializing North, but saw the war as no less inevitable.

In the wake of the First World War, though, revisionists like James Randall and Avery Craven argued that the Civil War was a terrible, avoidable blunder. Slavery was inefficient, and left alone, would have extinguished itself, they insisted—it was weak politicians and crumbling institutions that produced unnecessary bloodshed.

This was the reigning interpretation when Trump was in school; if he studied the causes of the Civil War, it’s likely what he would have learned. And asking the question does Trump no discredit; when I taught the history of the Civil War to lecture halls of college students, we spent weeks discussing it. What’s alarming is the answer he proposes; that the conflict might have been averted by a strong leader. And the omission of a critical word: slavery.

By the civil-rights era, historical interpretations of the war were shifting. Historians looked more closely at slavery, and saw a rapidly expanding, even thriving, system. They looked at the words of those who pushed the nation into war. And they concluded that there was a remarkably straightforward answer to the question posed by the president: “Why was there a Civil War? Why could that one not have been worked out?”

Because the Civil War was fought over slavery. “Our position is thoroughly identified with the institution of slavery—the greatest material interest of the world,” Mississippi declared as it seceded. “The people of the slave holding States are bound together by the same necessity and determination to preserve African slavery,” said Louisiana. “The servitude of the African race, as existing in these States, is mutually beneficial to both bond and free, and is abundantly authorized and justified by the experience of mankind, and the revealed will of the Almighty Creator, as recognized by all Christian nations,” insisted Texas.

And Lincoln understood it, too. “All knew that this interest was somehow the cause of the war,” he said. “To strengthen, perpetuate, and extend this interest was the object for which the insurgents would rend the Union even by war, while the Government claimed no right to do more than to restrict the territorial enlargement of it.”

The entirely uncontroversial consensus among professional historians is that slavery caused the war, although this conclusion has not reached much of the general public. Leaders like Jackson, then, only postponed the inevitable reckoning. It’s still tempting, though, to believe that the Civil War might have been avoided, the loss of three-quarters-of-a-million lives averted, the bloodiest conflict in our history forestalled. And for a century, many of America’s political leaders did everything in their power to turn a blind eye to the carnage of slavery, staving off sectional crises.

The first century of American history, in fact, can be told through the long litany of deals struck by strong leaders working to suppress, or at least delay, open conflict over slavery. The delegates in Philadelphia were deal makers; the Constitution they produced strengthened the federal government, but at the price of shielding slavery. The three-fifths compromise ensured the South would wield disproportionate power in the House and in presidential elections; the document protected the international slave trade for 20 years.

If some at the convention had hoped that compromise might buy enough time for slavery to pass out of existence on its own, they were disappointed. Instead, slavery—in all its horrifying brutality—became a cornerstone of American economic development. An ever-increasing number of human beings were held in bondage, their labor forcibly extracted, and their financial worth heavily leveraged.

The deals piled up, the list like a history-textbook index. The Missouri Compromise, in 1820. The Nullification Crisis in 1832. The Compromise of 1850. The Kansas-Nebraska Act, passed in 1854. Even on the eve of war, there was the failed Crittenden Compromise.

One hundred and sixty years ago, the founders of this magazine promised that, in politics, “It will deal frankly with persons and with parties, endeavoring always to keep in view that moral element which transcends all persons and parties, and which alone makes the basis of a true and lasting national prosperity.” Their point was that some issues aren’t personal, aren’t partisan, and aren’t amenable to compromise—that sometimes it is striking a deal which weakens a nation, and taking a principled stand which strengthens it.

There are some conflicts that a leader cannot suppress, no matter how strong he may be; some deals that should not be struck, no matter how alluring they may seem.

This was the great moral truth on which the Republican Party was founded.

Perhaps most people don’t know that.