What is huigu?

Some articles on huigu:

Princess Taihe - As Khatun
... Princess Taihe remained in Huigu, although it is not clear whether she remarried Zhaoli Khan or any other person ... to these wars, there was a major plague and major snow storm, causing great deaths of the Huigu livestock and leading to its sudden decline ... In 840, a major Xiajiasi attack on Huigu destroyed the Huigu headquarters, and both Yaoluoge Hesa and Jueluowu were killed in battle ...
Princess Taihe
... the Chinese Tang Dynasty and a Khatun (empress) of Huigu ... as part of the Heqin system of marriages between Tang princesses and Huigu khans, but suffered through Huigu's subsequent collapse before being welcomed back to the Tang court ...
Emperor Wuzong Of Tang - Reign - Dealing With The Huigu Incursions
... Wuzong had to deal with was the collapse of Tang's erstwhile vassal and ally Huigu — which had supported Tang in various campaigns through the decades ... In 840, due to internal power struggles, Huigu was weakened, such that when the Xiajiasi (Kirghiz) khan Are (阿熱) attacked, the Huigu khan Yaoluoge Hesa (藥羅葛闔馺) was killed ... The Huigu tribespeople scattered, fleeing in various directions ...
Li Jiang - During Emperor Xianzong's Reign - After Chancellorship
... For example, soon thereafter, he suggested that Huigu's proposal of having a Tang princess marry Huigu's Baoyi Khan, which Emperor Xianzong had declined previously due to the expenses ...