During the American Civil War, most of what is now the U.S. state of Oklahoma was designated as the Indian Territory. It served as an unorganized region that had been set aside specifically for Native American tribes and was occupied mostly by tribes which had been removed from their ancestral lands in the Southeastern United States following the Indian Removal Act of 1830. As part of the Trans-Mississippi Theater, the Indian Territory was the scene of numerous skirmishes and seven officially recognized battles involving both Native American units allied with the Confederate States of America and Native Americans loyal to the United States government, as well as other Union and Confederate troops.