The American Civil War began in 1861 following decades of tensions between northern and southern states over slavery and states' rights. Southern states seceded from the Union and formed the Confederate States of America after Abraham Lincoln was elected president. Major battles included Bull Run, Antietam, Gettysburg, Vicksburg, and Petersburg. The Union blockade and capture of the Mississippi River helped turn the tide. Ultimately, the war ended in 1865 with the Confederacy's surrender at Appomattox Courthouse after a long siege of Petersburg and Sherman's March to the Sea through Georgia and the Carolinas.