Battle of Talas 751
After the second unification of China under the Sui a period of prosperity followed under the Tang dynasty. The sound economy was accompanied by territorial expansion starting in 630.
The Tibetan tribes, for the first time, came under China's influence. Chinese power over Sinkiang was reestablished, extending Chinese control over the Silk road. Samarkand, Bukhara and parts of Afghanistan came under Chinese domination.
In the meantime the Arab empire spread like wildfire from Arabia after 635. The Arab armies overran Syria, Mesopotamia and Persia. Another army took Egypt and advanced into North Africa, crossing over to Spain. For the first time a world empire in the West clashed directly with the world empire in the East. In the battle of Talas in Central Asia (751)
Arab armies defeated the Chinese army decisively. But after that victory the Arabs did not advance any further because internal revolts started to weaken the agressive spirit that drove them for more than hundred years to conquest. Talas became therefore the demarcation line between the Muslim and Chinese world.