Kammala jumla mai zuwa: Buchanan ya karbi alƙawarinsa ga Jami'ar Sojan Amurka a West Point a lokacin gwamnatin Adams kuma ya kammala karatunsa a 1830. Ba da daɗewa ba aka sanya shi zuwa 4th Infantry na Amurka a matsayin mai ba da izini na biyu. Ayyukansa sun hada da sabis a cikin Black Hawk War (ya umurci gunboats a lokacin Battle of Bad Axe) da kuma a kan
Seminoles, kazalika da cire Cherokees zuwa yankin Indiya. An daukaka shi zuwa kyaftin a lokacin da yake aiki a Florida.