How do we know so much of Tang history today?

The Tang Dynasty ruled over a vast area that stretched from Korea to Northern Vietnam. It even reached west as far as Afghanistan. It took a very organized government to control all of this territory. The Tang established a detailed code of laws and administrative functions.

At the beginning of the sixth century A.D., north and south China were divided, but would be united through conquest by the Sui Dynasty, which ruled from 581 to 617 A.D

The Sui were led by General Yang Jian of the unified north. The Sui, however, lasted for only two emperors before falling to Li Yuan, founder of the Tang Dynasty.

Li Yuan was the cousin of the first Sui emperor and gained power during a period of mass rebellion after emerging from the northwest to beat other contenders for the throne. He ruled as Gaozu until 626 A.D. His son Taizong ascended the throne after killing his two brothers and several nephews.

In 630 A.D., Taizong seized a portion of Mongolia from the Turks and earned the title “Great Khan.” The Tangs made use of Turkish soldiers in an invasion of Khitan (far eastern Asia) and joint expeditions along the Silk Road.

Taizong also set up more aggressive systems to identify Confucian scholars and put them in civil service placements. He created Confucian state schools along with a sanctioned state version of The Five Classics, which also allowed talented scholars with no family connections to work their way up in the government.

Explanation:

it affected it because the kingdoms (with trade) slowly got richer and richer.