公元840年，回鹘汗国因自然灾害侵袭、统治集团内讧及黠戛斯(中国古族名)的进攻等原因而崩溃，其部众大部分向西迁徙。

• The Uighur Khanate collapsed in 840 because of natural disasters,internal strife and attacks by the ancient Jiegasi tribe. Consequently,most of the Uighur migrated westward.