When does behavioral theory first invented?

Behavioral theory, particularly in psychology, emerged in the early 20th century, with significant contributions from figures like John B. Watson, who published his influential paper "Psychology as the Behaviorist Views It" in 1913. This theory emphasized observable behaviors over internal mental states, aiming to establish psychology as a scientific discipline. B.F. Skinner later expanded on these ideas in the 1930s and 1940s, introducing concepts such as operant conditioning.