In the American Civil War (1861–65), the border states or the Border South were four, later five, slave states in the Upper South that primarily supported the Union. They were Delaware, Maryland, Kentucky, and Missouri, and after 1863, the new state of West Virginia. To their north they bordered free states of the Union, and all but Delaware bordered slave states of the Confederacy to their south.
Of the 34 U.S. states in 1861, nineteen were free states and fifteen were slave including the four border states; each of the latter held a comparatively low percentage of slaves. Delaware never declared for secession. Maryland was largely prevented from seceding by local unionists and federal troops. Two others, Kentucky and Missouri, saw rival governments, though their territory mostly stayed in Union control after 1862. Four others did not declare for secession until after the Battle of Fort Sumter and were briefly considered border states: Arkansas, North Carolina, Tennessee, and Virginia. They are called the Upper South, in contrast to the Deep South. A new border state was created during the war, West Virginia, which was formed from 50 counties of Virginia and became a new slave state in the Union in 1863 (with, initially, gradual abolition law).
