Until 1946, King Zahir ruled with the assistance of his uncle, who held the post of Prime Minister and continued the policies of Nadir Shah. Another of Zahir Shah's uncles, Shah Mahmud Khan, became Prime Minister in 1946 and began an experiment allowing greater political freedom, but reversed the policy when it went further than he expected. He was replaced in 1953 by Mohammed Daoud Khan, the king's cousin and brother-in-law, and a Pashtun nationalist who sought the creation of a Pashtunistan, leading to highly tense relations with Pakistan. During his ten years at the post until 1963, Daoud Khan pressed for social modernization reforms and sought a closer relationship with the Soviet Union. Afterward, the 1964 constitution was formed, and the first non-royal Prime Minister was sworn in.