As a historian, I know it’s nearly impossible to get everything right. No sooner does one write a chapter in a book than new research disproves at least some of the details of the “Corrupt Bargain”; new science, such as DNA testing, provides a clearer picture of who Jack the Ripper was or was not; and new techniques, such as mapping spent cartridges with metal detectors, allows for a different interpretation of “Custer’s Last Stand.”

Historians can, and should, debate both the big and small picture. Too often, however, modern historians have become consumed with painting a portrait of America that stretches or abuses the truth so badly that it distorts the past and produces a flawed, counterproductive view of America.

In my new book, “48 Liberal Lies About American History (That You Probably Learned in School),” I found many fallacies appearing regularly in 15 to 20 of the most common American history college textbooks. Not only did several of the textbooks use similar language, but the choice of images was itself telling of the liberal slant of these publications. For example, aside from Franklin Roosevelt and the atomic bomb, what might be the most common image representing life in the 20th century? Neil Armstrong’s lunar landing? Martin Luther King Jr.’s “I-have-a-dream” speech? John F. Kennedy?

Nope. The KKK. That’s right: In a majority of the books I examined, the third most common image in the 20th century section was a picture of the Klan. Yes, the Klan had a resurgence in the 1920s and it staged a march on Washington. Then it rapidly faded as a force. Which was more influential in 20th century politics — the Klan or the Right to Life movement, whose repeated marches on Washington numbered in the hundreds of thousands? You’ll look in vain for a single picture of a right-to-life march that isn’t accompanied by images of angry feminists shouting at the marchers in any of these textbooks.

Would it surprise you to know that most college textbooks refer to JFK’s killer, Lee Harvey Oswald, as a “quiet former Marine,” a “troubled former Marine,” or “having served in the Marines” — while only one identified him as a Communist?

Ever wonder why Harry Truman ordered the atomic bomb to be dropped on Japan? According to several of the new diplomatic history textbooks, Truman thought “because of the weapon, he did not need (or want) the Soviets to invade Manchuria or Japan.” Another said, “the use of the bomb would permit [the U.S.] to ‘out maneuver [sic] Stalin on China.'” Few of the textbooks mention the new, overpowering evidence from Japanese archives that disclose the war leadership of Japan was not budging on surrender until the bomb was dropped.

What about more recent history, history most of us can remember? Ronald Reagan was not elected because people agreed with his ideas. According to several of the books, he was elected because turnout was low. One textbook asks, “Where had all the voters gone? … the 1980s election reflected … ‘the largest mass movement of our time’ — nonvoting.” Another said, “In truth, the favorite candidate of millions of Americans, unhappy with Carter but distrustful of the right-wing ideologue Reagan, was ‘None of the above.'” Reagan defeated President Carter because Mr. Carter’s supporters just didn’t show up. Yet it is never commented upon that Reagan received 26.7% of the total electorate while President Clinton, considered a popular politician, won with only 23.6%.

Indeed, the Reagan years are the “pregnancy test” of liberal bias in a textbook, namely the section on the Reagan economy. A majority of the textbooks ignore employment and income growth, lower interest rates, and rising gross national product and instead focus almost entirely on deficits and debt. “The American Pageant” featured debt and deficit charts purporting to show that under Reagan the nation’s indebtedness skyrocketed, while concealing that they had not adjusted their data in real dollars. When I adjusted the numbers for real dollars as a share of GNP, Reagan’s debt levels were lower than those of presidents Kennedy, Eisenhower, Truman, and geometrically lower than FDR’s.

What about the Rosenbergs? One text says they were convicted in a “controversial trial” and the “controversy over their guilt has continued to the present day.” Perhaps the controversy has “continued,” but their guilt has been established beyond all doubt. Another textbook claims the case against the Rosenbergs “rested on the testimony of their supposed accomplices, some of them secretly coached by the FBI.” When in fact they were caught red-handed, so to speak, and no serious scholar doubts their guilt. According to another textbook: “Although they were not major spies and the information they revealed was not important, [they] were executed.” I guess we cannot believe the former premier of the Soviet Union, Nikita Khruschev, quoting his own no. 1 spymaster, when he said the Rosenbergs “provided very significant help in accelerating the production of our atom bomb.”

When wrapped together, these college textbooks go out of their way to advance anti-Americanism and to frame conservative ideas as backward whenever possible. Perhaps that’s why the first response by people when I tell them the title of my book, “48 Liberal Lies About American History,” is almost always the same: “only 48?”

Mr. Schweikart is a professor of History at the University of Dayton and is the author of “America’s Victories: Why the U.S. Wins Wars,” and co-author of “A Patriot’s History of the United States.” His most recent book, “48 Liberal Lies About American History,” was released this month by Sentinel HC.