Each summer, more than half a million tourists come to Gettysburg, a battlefield in the most divisive conflict in American history. After marching around in the heat, thousands stop in at Mr. G’s for some of the best ice cream in town. As they battle with their melting orange pineapple, they can look across the street to the new Unity Park and the newest of Gettysburg’s 1,300-plus monuments. Most commemorate battle; this one commemorates unity. It encourages a “focus on unity and peace.”

In the wake of an extremist’s assassination attempt at the congressional baseball practice, President Donald Trump once again called for unity because “our children deserve to grow up in a nation of safety and peace.” And in a February speech to Congress, he said he was delivering “a message of unity and strength. … We all salute the same, great American flag. … The time for trivial fights is behind us.”

The trouble with these pleas for unity is that sometimes unity lies.

The Unity Park monument mourns the “many young people from both the North and the South who sacrificed and endured so much for our country.” But those who sacrificed and endured for the Confederacy did not do it for “our country” but for their country — a country that wrote into its constitution that there could be no “law denying or impairing the right of property in negro slaves” and that slavery “shall be recognized and protected by Congress.”

Those who sacrificed and endured for the Union did so to end the Confederacy. A sign in Unity Park describes how a Confederate officer told 12-year-old Union musician Johnny Clem to surrender, but Clem wasn’t interested in “unity.” He shot the officer, and was promoted to sergeant. Apparently, young Johnny Clem knew that some differences aren’t trivial.

Lies that try to cover serious differences under the banner of unity mean somebody will get kicked to the curb. When this country pushed for unity after the Civil War, putting differences aside meant putting “problems” aside. And the problems were people: black people. Unity meant ignoring those white Southerners who lynched 4,000 people, burned Black Tulsa to the ground, robbed and murdered the black residents of Rosewood, and enshrined 100 years of racial terrorism across the South. Today, when Attorney General Jeff Sessions says stemming violent crime is a priority, using a one-year increase in crime to justify policies that produced decades of high incarceration rates, while ignoring decreases in crime in 22 of the last 26 years, we had better pay attention.

When executive orders and Department of Homeland Security memos lump together illegal immigration, drug trafficking, and violent crime without distinction of severity, when everything is framed as a “significant threat to national security and public safety,” and “a clear and present danger to the interests of the United States,” we had best be on high alert and figure out who will benefit and who will suffer. It won’t just be the undocumented that suffer: African-Americans should know from our history that our faces are the easiest ones to target as significant threats to security and safety.

In the decades after the Civil War, a series of U.S. Supreme Court rulings and executive policies that on their face had little to do with African-Americans ended up giving license to the incarceration, robbery and murder of thousands of black women and men.

W.E.B. Du Bois wrote, “The innocent, the guilty, and the depraved were herded together, children and adults, men and women, given into the complete control of practically irresponsible men, whose sole object was to make the most money possible. … Finally the state became a dealer in crime.”

Now put this in today’s context. Sessions has already reversed phasing out private prisons and one of Trump’s executive orders encourages the government to “establish contracts to construct, operate, or control facilities to detain aliens.” Since Trump’s election and Sessions’ appointment, stock in the two major private prison companies has shot up.

When the post-Reconstruction North and South mixed together “law and order” with profit and publicly agreed to put “their differences” behind them in pursuit of unity and stability, African-Americans just got criminalized in new ways. A black man looking for work, passing through a Southern town, stopping on a street corner for some shade and a cool drink, could get arrested for loitering. And then charged for “room and board” while in jail. So he had to pay a fine and pay for the food and miserable living conditions. So he’d have to work. And get paid next to nothing. But private companies who hired out prison labor got cheap workers. More prisoners meant more money for private companies and for the state. And a shorter life span for black prisoners.

So when leaders start emphasizing unity while at the same time using a language of fear, crime, safety and security, we best perk up our ears. Unity matters — it’s a goal worth working toward. But regardless of its worth or the sincerity of those who call for it, we should be asking who will be sacrificed to achieve it.

Because sometimes unity kills.

Scott Hancock is an associate professor of history and Africana studies at Gettysburg College. He wrote this for The Philadelphia Inquirer.