In one of my opinion columns for The Horn, I advocated removing the statues of Confederate leaders from the University of Texas at Austin’s campus. I’ve been surprised and disappointed by how many people are truly proud of our Confederate history. Many believe that slavery wasn’t the main cause of the Civil War, and that the Southerners were fighting “about autonomy/ freedom from a authoritarian government,” as one commenter wrote.

In fact, a survey conducted by the Pew Research Center in 2011 found that 48% of Americans considered states’ rights to be the primary cause of the war, compared to only 38% who said the war was mainly about slavery.

However, the vast majority of historians today, as well as firsthand accounts from the time, point out that slavery was undoubtedly the primary factor of the American Civil War (although, of course, not the only cause).

According to Dr. Drew Gilpin Faust, historian and president of Harvard University, “Historians are pretty united on the cause of the Civil War being slavery.”

James McPherson, a Princeton Civil War historian and author of the Pulitzer Prize-winning history Battle Cry of Freedom, made an even bolder claim: “Probably 90 percent, maybe 95 percent of serious historians of the Civil War would agree on the broad questions of what the war was about and what brought it about and what caused it, which was the increasing polarization of the country between the free states and the slave states over issues of slavery, especially the expansion of slavery.”

As Dr. Walter Edgar, a historian at the University of South Carolina, stated, “Go back to what the 169 men who voted to secede first from the Union said, and in their declaration of causes, that it was — said it was protect slavery and their other domestic institutions.”

But let’s say that today’s historians are out of touch with that period of time. What’d the people who lived back then consider to be the cause of the war?

In 1863, Senator Charles Sumner from Massachusetts stated, “[T]here are two apparent rudiments to this war. One is Slavery and the other is State Rights. But the latter is only a cover for the former. If Slavery were out of the way there would be no trouble from State Rights. The war, then, is for Slavery, and nothing else.”

President Abraham Lincoln in his Second Inaugural Address: “These slaves constituted a peculiar and powerful interest. All knew that this interest was somehow the cause of the war.”

But Lincoln and Sumner were Northerners, loyal to the Union, so of course they’d say that, right? What’d the Southerners themselves think the war was about?

L.W. Spratt, editor of The Charleston Mercury, markedly wrote in 1861, “The South is now in the formation of a Slave Republic.”

But Spratt was a journalist so he wasn’t directly involved with the CSA, right? So what were the stated reasons of the actual politicians who took official action to secede?

Shortly after seceding from the Union in 1860, the state of South Carolina adopted a document which they titled the “Declaration of the Immediate Causes which Induce and Justify the Secession of South Carolina from the Federal Union.” In the “Declaration of the Immediate Causes,” the key cause was “an increasing hostility on the part of the non-slaveholding States to the institution of slavery.” Non-slaveholding states, according to the document, “have denied the rights of property established in fifteen of the States and recognized by the Constitution; they have denounced as sinful the institution of slavery; they have permitted open establishment among them of societies, whose avowed object is to disturb the peace and to eloign the property of the citizens of other States. They have encouraged and assisted thousands of our slaves to leave their homes; and those who remain, have been incited by emissaries, books and pictures to servile insurrection.” They are very clear that the “Immediate Causes which Induce and Justify the Secession” revolve around their ‘property rights,’ aka their right to own enslaved human beings.

And it wasn’t just South Carolina that made it clear that slavery was a huge factor in their decision to secede – Texas and other states made it clear as well (You can read some of the states’ reasons, in their own words, here).

The leadership of the Confederacy made their reasoning clear as well. In 1861, Vice President of the Confederate States of America, Alexander Stephens, in his Cornerstone Speech, declared “[T]he new Constitution [of the Confederate States of America] has put at rest forever all the agitating questions relating to our peculiar institutions—African slavery as it exists among us—the proper status of the negro in our form of civilization. This was the immediate cause of the late rupture and present revolution.”

And if you’re still skeptical, even the 1861 Constitution of the Confederate States explicitly defends slavery: “In all such territory the institution of negro slavery, as it now exists in the Confederate States, shall be recognized and protected be Congress and by the Territorial government.”

I’m not claiming that slavery was the only cause of the Civil War, but it was unquestionably the main cause. After all, we have had heated disagreements over states’ rights throughout our nation’s history, and we will continue to have such debates in the future. But only one issue led us into a Civil War: slavery.