The United States Civil War lasted from 1861 to 1865 and was caused by differences between the northern and southern states over the issue of slavery. Abraham Lincoln was elected president in 1860 representing the northern states, while Jefferson Davis became president of the southern Confederate states. Key battles included Fort Sumter, Bull Run, Vicksburg, Antietam, and Gettysburg, with the Union eventually prevailing and bringing an end to slavery while over half a million soldiers were killed or wounded.