The Sabzevar expedition was a politically decisive event in Nader's career where he in effect turned from mere commander-in-chief of Tahmasp's forces into the real power behind the throne (although technically this still was a government in exile as the Gilzai Afghans were in control of Isfahan). The expedition was launched mainly due to Tahmasp's own incompetence and ill-thought attempt at curbing the powers of his upstart general and military genius.