The Muslim conquest of Persia, also known as the Arab conquest of Iran, led to the end of the Sasanian Empire in 651 and the eventual decline of the Zoroastrian religion in Iran. The rise of Muslims coincided with a significant political, social, economic and military weakness in Persia. Once a major world power, the Sasanian Empire had exhausted its human and material resources after decades of warfare against the Byzantine Empire. The internal political situation quickly deteriorated after the execution of King Khosrau II on February 28, 628. Subsequently, ten new claimants were enthroned within the next four years, highlighting the political instability of the Sassanians prior to the Muslim invasion.