Tang's Four Garrisons of Anxi and Administration of the Western Regions

Timeline

1. 701–750Kucha · Western RegionsThe Tang made Kucha the seat of the Anxi Protectorate; the four garrisons (Kucha, Karashahr, Khotan, Kashgar) each held heavy garrisons controlling the north and south flanks of the Tarim Basin and the central Silk Road route.
2. 751Talas · Central AsiaTang forces clashed with Arab Abbasid troops at Talas and were defeated. Though the battle did not directly change control of the Western Regions, it marked the obstruction of Tang westward expansion and the beginning of a shift in Central Asia's balance of power.
3. 755–800Hexi Corridor · GansuAfter the An Lushan Rebellion, Tang forces in the northwest were recalled inland; Tibet seized the Hexi Corridor and Longyou, cutting the Four Garrisons off from the Central Plains until they became isolated outposts, and by the late 8th century the Tang had essentially lost control of the Western Regions.