During the American Civil War, the Union, also known as the North, referred to the United States, governed by the U.S. federal government led by President Abraham Lincoln. It was opposed by the secessionist Confederate States of America (CSA), informally called "the Confederacy" or "the South". The Union is named after its declared goal of preserving the United States as a constitutional union. "Union" is used in the U.S. Constitution to refer to the founding formation of the people, and to the states in union. In the context of the Civil War, it has also often been used as a synonym for "the northern states loyal to the United States government;" in this meaning, the Union consisted of 20 free states and five border states.