Irreconcilable sectional conflict regarding the enslavement of Africans and African Americans ultimately led to the American Civil War.[98] With the 1860 election of Republican Abraham Lincoln, conventions in thirteen slave states declared secession and formed the Confederate States of America (the "South" or the "Confederacy"), while the federal government (the "Union") maintained that secession was illegal.[99] In order to bring about this secession, military action was initiated by the secessionists, and the Union responded in kind. The ensuing war would become the deadliest military conflict in American history, resulting in the deaths of approximately 620,000 soldiers as well as upwards of 50,000 civilians.[100] The Union initially simply fought to keep the country united. Nevertheless, as casualties mounted after 1863 and Lincoln delivered his Emancipation Proclamation, the main purpose of the war from the Union's viewpoint became the abolition of slavery. Indeed, when the Union ultimately won the war in April 1865, each of the states in the defeated South was required to ratify the Thirteenth Amendment, which prohibited slavery except as penal labor. Two other amendments were also ratified, ensuring citizenship and voting rights for blacks.
Reconstruction began in earnest following the war. While President Lincoln attempted to foster friendship and forgiveness between the Union and the former Confederacy, his assassination on April 14, 1865 drove a wedge between North and South again. Republicans in the federal government made it their goal to oversee the rebuilding of the South and to ensure the rights of African Americans. They persisted until the Compromise of 1877 when the Republicans agreed to cease protecting the rights of African Americans in the South in order for Democrats to concede the presidential election of 1876.
Southern white Democrats, calling themselves "Redeemers", took control of the South after the end of Reconstruction, beginning the nadir of American race relations. From 1890 to 1910, the Redeemers established so-called Jim Crow laws, disenfranchising most blacks and some impoverished whites throughout the region. Blacks would face racial segregation nationwide, especially in the South.[101] They also occasionally experienced vigilante violence, including lynching.[102]