Caliph Al-Saffah died in the year 752 AD. Chinese sources record that his successor, the Abbasid caliph Al-Mansur, sent his diplomatic delegations regularly to China. Al-Mansur's delegations were known in China as "Khayi Tashi" ("Black Clothes"). Shortly after the battle of Talas, the domestic An Lushan rebellion and subsequent warlordism gave the Arabs the opportunity to further expand into Central Asia as Tang influence in the region retreated. The An Lushan Rebellion started in 755 and lasted until 763, forcing the Tang army to retreat from the Xinjiang after enjoying around 100 years of sovereignty. This effectively ended the Tang Chinese presence in Central Asia. In 756 Al-Mansur sent more than 22,000 Arab mercenaries to assist Emperor Xuanzong of Tang in the An Lushan rebellion. The Muslim population of Ningxia are considered descendants of the Arab soldiers who settled after Chang'an was recaptured.