American Civil War: Arkansas secedes from the Union.

The American Civil War was a civil war in the United States between the Union and the Confederacy, which was formed in 1861 by states that had seceded from the Union. The central conflict leading to war was a dispute over whether slavery should be permitted to expand into the western territories, leading to more slave states, or be prohibited from doing so, which many believed would place slavery on a course of ultimate extinction.

During the American Civil War, Arkansas was a Confederate state, though it had initially voted to remain in the Union. Following the capture of Fort Sumter in April 1861, Abraham Lincoln called for troops from every Union state to put down the rebellion, and Arkansas along with several other southern states seceded. For the rest of the civil war, Arkansas played a major role in controlling the Mississippi River, a major waterway.

The Union was the central government of the United States during the American Civil War. Its civilian and military forces resisted the Confederacy's attempt to secede following the election of Abraham Lincoln as president of the United States. Lincoln's administration asserted the permanency of the federal government and the continuity of the United States Constitution.