Forsyth remained in the Regular Army after the end of the Civil War. He commanded a brigade of cavalry for two years and was a strong supporter of African Americans and buffalo soldiers. He then joined Sheridan again in 1867, and moved with him when he became commander of the Department of the Missouri in 1866. Forsyth served first as the department's secretary and then as inspector, with an appointment in the cavalry. He took part in military campaigns against the Comanche, Cheyenne, Arapaho, and Kiowa Indians in 1868–69. Forsyth went to Europe in 1870 as an official observer of the Franco-Prussian War.