The war was fought to keep the United States united. It began because the southern states kept slaves to work in the cotton fields. Slaves were not allowed in the North, and the two sides argued about whether they should allow them in the new lands of the West. In 1860, Abraham Lincoln, who belonged to the Republican party, which was against keeping slaves, was elected president. On December 24, South Carolina said that it wanted to be independent and the other southern states soon followed; they called themselves the 'Confederate States of America'. The fighting began on April 12 1861, at Fort Sumter.