In 1840, Reid moved to Missouri, where he taught school and studied law. He was admitted to the Missouri bar and commenced practice in
Jefferson City in 1844. A captain in the Mexican War, Reid led a company that served in Doniphan's Regiment where he participated in the
Battle of Sacramento. During the war, he was wounded twice. He also participated in an expedition against the
Navajo in
New Mexico. Back in Missouri, Reid participated in raids against abolitionists in Kansas. He led 200 pro-slavery raiders in August 1856 in what became known as the
Battle of Osawatomie, in which later-famous
John Brown's son Frederick was among the six free-staters killed; two pro-slavery raiders also died. Reid led the pro-slavery forces that Governor (and later Union General)
John W. Geary ordered to disperse from
Lawrence, Kansas in September 1856. Jackson County voters elected Reid to the Missouri House of Representatives, and he served from 1854 to 1856, as well as helped revise the state's statutes. He bought land near the junction of the
Missouri and
Kansas Rivers in what became
Kansas City in 1856, and helped organize the frontier town's Chamber of Commerce in 1857. Reid made a fortune from his resumed legal practice as well as banking and real estate. ==Death and legacy==