Hostilities began on April 12, 1861, when Confederate forces fired upon Fort Sumter, a key fort held by Union troops in South Carolina. Lincoln called for every state to provide troops to retake the fort; consequently, four more slave states joined the Confederacy, bringing their total to eleven. Lincoln soon controlled the border states, after arresting state legislators and suspending habeas corpus, ignoring the ruling of the Supreme Court's Chief Justice that such suspension was unconstitutional, and established a naval blockade that crippled the southern economy. The Eastern Theater was inconclusive in 1861–62. The autumn 1862 Confederate campaign into Maryland ended with Confederate retreat at the Battle of Antietam, dissuading British intervention. To the west, by summer 1862 the Union destroyed the Confederate river navy, then much of their western armies, and the Union siege of Vicksburg split the Confederacy in two at the Mississippi River. In 1863, Robert E. Lee's Confederate incursion north ended at the Battle of Gettysburg. Lincoln issued the Emancipation Proclamation, which made ending slavery a war goal.
Causes of secession
The causes of the Civil War were complex and have been