Vygotsky was Soviet psychologist when there was a Soviet Union. Because the Soviet Union was a closed society and Vygotsky did not know what advancements were made in psychology in the rest of the world, he developed a theory of cognitive development similar to the one Piaget developed. His theory, however, had to comply with Pavlov's theory of psychology and classical conditioning, because it was a political requirement of his profession (Pavlov was a hero in Soviet science). So, his theory differes from Piaget's theory in that he pays tribute to Pavlov by showing a connection to his theory. His theory proved more amenable to the development of treatments for children. While Piaget felt little need to try to encourage progress through his stages, Vygotsky's theories offered some connection with training methods.