As the United States moved west, the issue of slavery was intensifying strains between the rapidly industrializing North and the slave-based agricultural South. The South was determined to maintain the institution of black slavery against the federal government's efforts to curtail the latter's spread. Several compromises over the slavery issue held the Union together for more than a half-century, but the election as president in 1860 of Abraham Lincoln, whose Republican Party clearly advocated the prohibition of slavery in the Western territories, led South Carolina to secede, joined by 10 other Southern states by the next year.
Lincoln denied the Southern states' right to secede. The North's defeat of the South in the ensuing Civil War (1861-65) resulted in the preservation of the Union, the abolition of slavery, the establishment of citizenship for former slaves, and the institution of universal adult male suffrage. Lincoln's plans for magnanimity to the defeated South were cut short by his assassination, and Congress, completely dominated by northern Radical Republicans, embarked on its own, more punitive scheme of reconstruction. This system, which protected black civil rights in the South, came to an end with the withdrawal of federal (Northern) troops by 1877. Thereafter, Southern blacks were gradually disenfranchised and forcibly segregated within the larger society.
