The American Civil War (1861–1865), also known as the War Between the States as well as several other names, was a civil war in the United States of America. Eleven Southern slave states declared their secession from the United States and formed the Confederate States of America, also known as "the Confederacy". Led by Jefferson Davis, they fought against the United States (the Union), which was supported by all the free states and the five border slave states.
In the presidential election of 1860, the Republican Party, led by Abraham Lincoln, had campaigned against the expansion of slavery beyond the states in which it already existed. The Republican victory in that election resulted in seven Southern states declaring their secession from the Union even before Lincoln took office on March 4, 1861. Both the outgoing administration of President James Buchanan and Lincoln's incoming administration rejected the legality of secession, considering it rebellion.