The Sui dynasty was founded in northenn China in 581 AD and had reunited the whole counfty by 589. After a disastrous war with Koguryo Korea and several rebellions, the new T’ang dynasty united China by 623 and extended Chinese frontiers further than ever before.
Sui and early T’ang armies were based on the Fu-ping militia conscription system.
T'ang armies in the steppes were composed entirely of cavalry, mostly Turkish auxiliaries. T'ang armies in Central Asia had all their infantry mounted. Round shields were adopted under central asian influence. T’ang infantry were divided into pu-ping "marching infantry" and pu-she “foot archers". Some Sui cavalry carried lance, others sword and shield. Under the T’ang, most heavy cavalry were armed in Turkish style with lamellar armour, lance and bow. The use of horse armor declined under the T'ang, restricred to few elite units. Mounted crossbowmen were re-introduced by the T'ang. Mo-ho alies are the Manchurian tribes called Malgal by the Koreans. Didn't include any "cord and plaque" armor, its a wip.
The T'ang conquered the Eastern Gokturks in 630 and the Western Gokturks in 657.
The battle of Talas defeat against the Abbasid Caliphate and its ally, the Tibetan Empire in 751 marked the end of the Tang westward expansion. The T'ang were rocked by the great rebellion of An Lu-shan in 755 AD, and never fully recovered.