The Civil War was caused by several factors including disputes over states' rights versus federal authority, economic differences between the industrial North and agricultural South, and the issue of slavery. Key battles such as Antietam, Gettysburg, and Vicksburg resulted in massive casualties and shifted momentum between the Union and Confederacy over the course of the four-year war. General Ulysses S. Grant employed successful strategies in the Western Theater that helped the Union gain control of the Mississippi River and contributed to the eventual surrender of Confederate General Robert E. Lee at Appomattox Courthouse in 1865, marking the end of the Civil War.