In the 1850s, The northern and southern states were divided over the expansion of slavery into new territories acquired by the United States. Northerners were largely against the expansion of slavery, while Southerners were in favor of it. This conflict led to a series of events, including the Compromise of 1850 and the Kansas-Nebraska Act, which further strained relations between the two regions.
In 1860, Abraham Lincoln was elected president, on a platform that was opposed to the expansion of slavery into the territories. This election resulted in the secession of seven Southern states (South Carolina, Mississippi, Florida, Alabama, Georgia, Louisiana, and Texas). They argued that the new federal administration would infringe upon their rights as states to maintain slavery. Over time, four additional Southern states (Virginia, Arkansas, Tennessee, and North Carolina) also seceded, bringing the total number of seceded states to eleven.
The secession of the Southern states led to the American Civil War, which lasted from 1861 to 1865. The Union victory in the Civil War resulted in the abolition of slavery and the reunification of the country.