Montana in the American Civil War Montana in the American Civil War The area that eventually became the U.S. state of Montana played little direct role in the American Civil War. The closest the Confederate States Army ever came to the area was New Mexico and eastern Kansas, each over a thousand miles away. There was not even an organized territory using "Montana" until the Montana Territory was created on May 26, 1864, three years after the Battle of Fort Sumter. In 1861, the area was divided between the Dakota Territory and the Washington Territory, and in 1863, it was part of the Idaho Territory. Nevertheless,
Trans-Mississippi Theater of the American Civil War representatives on June 23, 1865. Trans-Mississippi Theater of the American Civil War The Trans-Mississippi Theater of the American Civil War consists of the major military operations west of the Mississippi River. The area is often thought of as excluding the states and territories bordering the Pacific Ocean, which formed the Pacific Coast Theater of the American Civil War (1861-1865). The campaign classification established by the National Park Service of the U.S. Department of the Interior is more fine-grained than the one used in this article. Some minor NPS campaigns have been omitted and some have been combined into larger categories.