There's no question: the Civil War was about slavery. Denying the central role that slavery played in the Civil War goes against all the facts. And yet some still cling to the revisionist history argument that the South wanted independence or lower taxes, or fought for states' rights. But history shows that states' rights meant the right to own slaves.
How did slavery cause the Civil War? For decades before the war, Americans became increasingly polarized over the question of slavery, as the number of slaves increased in the South and decreased in the North. Westward expansion created a new battleground over slavery, with slave states promoting the expansion of the "peculiar institution" into new territories like Missouri, Kansas, and California. Abraham Lincoln predicted that slavery would split the country, and a shocking map convinced him that slavery had to end. Finally, the abolition of slavery was a condition of the Confederate surrender at Appomattox.
History before, during, and after the Civil War proves that the war was about slavery. Anyone who still doubts what the Civil War was really about should listen to the words of Confederates and former slaves - both groups agreed on this point.
After the Fugitive Slave Act of 1850 and the Kansas-Nebraska Act of 1854, a violent confrontation over slavery was inevitable. The 1857 Dred Scott case pushed the country even closer to the brink of war. Dred Scott was a slave whose owner moved him into current-day Minnesota, a territory which had outlawed slavery. After years living there, Scott tried suing for his freedom.
The Supreme Court ruled that Black Americans were not citizens and thus had no right to sue. The ruling set a precedent denying all freed Blacks the rights and protections of American citizenship. Further, the court decided that the federal government could not prohibit slavery in the territories - overturning multiple compromises that attempted to keep the peace between the increasingly anti-slavery North and the pro-slavery South.
In 1860 and 1861, 11 states seceded from the Union, with the new Confederate states writing documents justifying their treasonous act. South Carolina, for example, adopted the "Declaration of the Immediate Causes Which Induce and Justify the Secession of South Carolina from the Federal Union" on December 24, 1860. It pointed to “an increasing hostility on the part of the non-slaveholding States to the institution of slavery," further arguing that Northern states no longer returned fugitive slaves (as the Constitution required).
Similarly, Mississippi's secession declaration of January 9, 1861, stated, “Our position is thoroughly identified with the institution of slavery - the greatest material interest of the world." Slavery, they argued, was worth defending in a civil war. "Its labor supplies the product which constitutes by far the largest and most important portions of the commerce of the earth... A blow at slavery is a blow at commerce and civilization.”
Just after the rise of the Confederacy, a map of slaves in the south provided visual proof of the region's dependence on slavery. The 1861 map, produced using census reports from the previous year, showed the percentage of slaves in each county. In some areas, they made up over 90% of the population.
The map shaped President Lincoln's response to the rebelling states, showing which areas might have less allegiance to the Confederacy and the institution of slavery. And as Lincoln moved toward the idea of emancipation, he used the map to understand what Union troops might face after slavery ended. As the map showed, many parts of the South might cease to exist without slave labor.
In 1858, Lincoln declared in his "House Divided" speech that slavery had to end - or it would overtake the country. He posited:
Either the opponents of slavery will arrest the further spread of it and place it where the public mind shall rest in the belief that it is in the course of ultimate extinction, or its advocates will push it forward till it shall become alike lawful in all the states, old as well as new, North as well as South.
Lincoln was personally against slavery, though in the early years of the Civil War he proclaimed that saving the Union was more important than ending the practice. In August 1862, Lincoln wrote, "If I could save the Union without freeing any slave, I would do it; and if I could save it by freeing all the slaves, I would do it; and if I could save it by freeing some and leaving others alone, I would also do that." Just a month later, after the bloody battle of Antietam, Lincoln issued his Emancipation Proclamation, declaring slavery could not continue.