The American Civil War (1861–1865), also known as the War Between the States, refers to the conflict that ensued between the US Federal government and eleven Southern slave states that seceded from the United States to form the Confederate States of America ("the Confederacy"). Led by its president, Jefferson Davis, the Confederacy fought to be independent from the United States and retain slavery. The U.S. federal government, led by President Abraham Lincoln, was supported by twenty mostly-Northern free states where slavery had already been illegal, and by five slave states that became known as the border states. These twenty-five states, referred to as the Union, had a much larger population and much more industry than the South. After four years of bloody, devastating war (mostly in the South), the Confederacy surrendered and slavery was abolished throughout the reunited nation. With the union's victory, the United States was restored. The postwar period, known as the Reconstruction era, lasted from 1865 through 1877.