After returning to his district, Yakir continued military reform. He was one of the creators of the first large tank and air force formations in the world. Not a military theorist in his own right, Yakir strongly supported Tukhachevsky's endeavor in developing the theory of deep operations. Military historians across the world still consider this theory an outstanding theoretical innovation. In 1934 Yakir requested that Tukhachevsky would be appointed to conduct advanced courses on operational theory for high-ranking officers of the Red Army General Staff and commanders of military districts. He did it even though he knew about Joseph Stalin's dislike of Tukhachevsky. In retribution, Stalin instructed Kliment Voroshilov, the Peoples Commissar of Defense, to bar Yakir from membership in the prestigious Advisory Council of the Defense Commissariat. In 1935, in order to diminish Yakir's power, the Ukrainian Military District was divided into two new districts: Kiev, under Yakir's command, and Kharkov.