The New Mexico Territory, which included the areas which became the modern U.S. states of New Mexico and Arizona as well as the southern part of present-day Nevada, played a small but significant role in the Trans-Mississippi Theater of the American Civil War. Despite its remoteness from the major battlefields of the east and its existence on the still sparsely populated and largely undeveloped American frontier, both Confederate and Union governments claimed ownership over the territory, and several important battles and military operations took place in the region.