The American Civil War (also known by other names) was a civil war in the United States from 1861 to 1865, fought between the northern United States (loyal to the Union) and the southern United States (that had seceded from the Union and formed the Confederacy). The civil war began primarily as a result of the long-standing controversy over the enslavement of black people. War broke out in April 1861 when secessionist forces attacked Fort Sumter in South Carolina shortly after Abraham Lincoln had been inaugurated as the President of the United States. The loyalists of the Union in the North, which also included some geographically western and southern states, proclaimed support for the Constitution. They faced secessionists of the Confederate States in the South, who advocated for states' rights in order to uphold slavery.