The election of a Republican president opposed to the expansion of slavery into the western territories led seven states in the lower South to secede from the Union and to establish the Confederate States of America. After Lincoln notified South Carolina’s governor that he intended to resupply Fort Sumter in Charleston harbor, the Confederacy fired on the installation, leading the President to declare that an insurrection existed in the South.

Early in the war, the Union succeeded in blockading Confederate harbors, and by mid-July 1862 it had divided the Confederacy in two by wresting control of Kentucky, Missouri, and much of Tennessee, as well as Mississippi River. In the Eastern Theater in 1861 and 1862, the Confederacy stopped Union attempts to capture its capital in Richmond, Virginia. In September 1862 (at Antietam in Maryland) and July 1863 (at Gettysburg in Pennsylvania), Robert E. Lee tried and failed to provoke European powers intervention in the war by winning a victory on Northern soil.

After futile pleas to the border states to free slaves voluntarily, Lincoln in the summer of 1862 decided that emancipation was a military and political necessity. The Emancipation Proclamation transformed the war from a conflict to save the Union to a war to abolish slavery. It also authorized the enlistment of African Americans. During the war Congress enacted the Homestead Act offered free public land to western settlers; and land grants supported construction of a transcontinental railroad. The government also raised the tariff, enacted the first income tax, and established a system of federally-chartered banks.