1922 — American Chiropractic Association is formed. The first national chiropractic association, the ACA, was formed by three disciples of D. D. Palmer: Solon M. Langworthy, Oakley G. Smith, and Minora C. Paxon, who also published the first chiropractic textbook (see 1906). Sometime in the 1930s, this organization combined with the National Association of Chiropractic Doctors, which had been established in 1904.

Three subsequent organizations would use the name American Chiropractic Association. The modern ACA was formed in 1963 (see 1963.).