Emperor Taizong of the Tang Dynasty begins…

Emperor Taizong of the Tang Dynasty begins a campaign against the Xiyu states in the Tarim Basin.

Qu Wentai, the king of Gaochang, a Xiyu state n the Tarim Basin, around the new year of 640 forms an alliance with Western Tujues who are hostile to Tang.

Emperor Taizong sends Hou Junji, assisted by Xue Wanjun, to attack Gaochang.

Qu Wentai, when Hou arrives at Gaochang, dies and is succeeded by his son Qu Zhisheng.

Rejecting a proposal by some of his generals to ambush the Gaochang nobles when they are burying Qu Wentai (finding that doing so would be immoral), he puts Gaochang's capital under siege, forcing Qu Zhisheng to surrender.

Emperor Taizong annexes Gaochang territory except for three cities, which Gaochang had seized from Yanqi, and which are therefore returned to Yanqi after the king of Yanqi meets with Hou to congratulate him.

Hou returns to the Tang capital Chang'an with Qu Zhisheng and his subordinates as captives.