When the U.S. Army in 1866 sent troops to build a string of forts along the Bozeman Trail north from the North Platte River to the Montana gold fields, Lakota, Cheyenne and Arapaho tribes in that country reacted angrily. For two years, the tribes harassed and attacked the soldiers and travelers on the trail. After the Treaty of Fort Laramie in 1868, the Army withdrew, the Indians burnt the forts and for a few years, until hostilities started up again in the mid-1870s, the tribes the country largely to themselves.