In the Summer of 751, Chinese and Arabs fought a defining battle for domination of Central Asia.
Kao Hsien-chih marched in with his troops and Qarluq auxiliaries as well as a contingent gent from Fergana. As the two adversaries met in battle at the end of July near Taraz, the Qarluq switched sides. The Chinese were crushed, and Kao Hsien-chih barely escaped. The Arabs' victory had more lasting and far-reaching consequences than this relatively obscure battle seemed to promise, for China never again ventured to claim mastery over territories beyond Sinkiang - with minor exceptions during the rule of the last dynasty to rule China, that of the Ching (Manchus), as we shall relate in due course.
Svat Soucek. A History of Inner Asia (Kindle Locations 1027-1030). Kindle Edition.
Aside from the obvious geopolitical consequences:
The Arab victory of 751 had yet another consequence: the victors captured a certain number of Chinese, some of whom were expert at manufacturing paper, an art practiced in China but unknown in the West. The Arabs were quick to learn from their captives, and paper manufacture spread throughout the Islamic world from where it also reached Christian Europe.
Svat Soucek. A History of Inner Asia (Kindle Locations 1036-1038). Kindle Edition.
If you are reading this (albeit electronically), you might thank Quarlug treachery.