The Unauthorized Regiment (formally the 1st Montana Volunteer Cavalry Regiment) was a group of volunteers led by Colonel Theodore Roosevelt to patrol the United States border with the Dominion of Canada during the Second Mexican War. They fought the Anglo-Canadian army, commanded by General C.G. Gordon, that invaded Montana Territory from Canada. In conjunction with George Armstrong Custer's Army Regulars, Roosevelt's Unauthorized Regiment inflicted a crushing defeat on Gordon's army. In the 1930s, a movie about the Unauthorized Regiment was made with Marion Morrison starring as Roosevelt.