c.1500, "to make into one," from M.Fr. unifier (14c.), from L.L. unificare "make one," from L. uni- "one" (see uni-) + root of facere "to make" (see factitious). Unification is attested from 1851; the Unification Church was founded 1954 in Korea
by Sun Myung Moon. Unified is attested from 1862. Unified (field) theory in physics is recorded from 1935.