Where did the Civil War take place?

The US Civil War took place in the states bordering the arbitrary division between the "Northern" (Union) states and the "Southern" (Confederate) states. The capitals of the respective combatants, Washington DC and Richmond, VA, were only 96 miles (154 km) apart, but were defended when attacked.

Maryland and the District of Columbia were secured by the Union, chiefly by imprisoning the officials there with Confederate sympathies. West Virginia, controlled by the Union, was split into a separate state in 1863 as a result of the war.

The only major engagements within the North were in the border states of Kentucky, Pennsylvania, Maryland, and West Virginia. These included Antietam in Maryland (September, 1862) and Gettysburg, PA (July, 1863). By the war's end, most of the Southern states had been attacked and overrun by Union armies, notably those of Ulysses S. Grant and William T. Sherman.

Opposing States

The Confederate States were:
Texas, Louisiana, Arkansas, Mississippi, Alabama, Georgia, Florida, South Carolina, North Carolina, Tennessee, and Virginia.
The Union States were:
California, Connecticut, Delaware, Illinois, Indiana, Iowa, Kansas, Kentucky*, Maine, Maryland, Massachusetts, Michigan, Minnesota, Missouri*, Nevada (1864), New Hampshire, New Jersey, New York, Ohio, Oregon, Pennsylvania, Rhode Island, Vermont, West Virginia, and Wisconsin.

(* = pro-Southern secessionists had separate state governments during the war)