The Civil War was fought from 1861 to 1865 between the Union (Northern) states and the Confederate (Southern) states. Slavery and states' rights were at the core of tensions between the North and South that led to war. Key battles included Fort Sumter, Antietam, Gettysburg, and Sherman's March to the Sea. The war ended in 1865 with the surrender of Confederate forces and the assassination of President Abraham Lincoln, who had issued the Emancipation Proclamation freeing all slaves. Over 600,000 soldiers lost their lives in the Civil War, which preserved the United States as one nation and led to the abolition of slavery.