In 638, Tufan's Songtsän Gampo, after hearing that the rulers of Tujue and Tuyuhun were all able to marry Tang princesses, requested to marry one as well, but was rebuffed by Emperor Taizong.
Around the new year of 640, Qu Wentai (麴文泰), the king of Gaochang, formed an alliance with Western Tujues who are hostile to Tang.