Behaviorism is a theory of learning based on the idea that all behaviors are acquired through conditioning and interaction with the environment. It was formally established in 1913 and became the dominant school of thought in psychology from 1920-1950s due to its objective and measurable approach. There are two main types of behaviorism: methodological behaviorism which studies observable behavior scientifically without mental states, and radical behaviorism which understands behavior through environmental reinforcements. The two major types of conditioning are classical conditioning which pairs stimuli to elicit responses, and operant conditioning where behaviors are reinforced or punished through consequences to make them more or less likely to occur again.