In 610, when Emperor Yang visited the headquarters of Ashina Rangan—who had, by this point, with Sui support, become the ruler of the Eastern Turkic Khaganate ("Dong Tujue")—the emissary from Goguryeo happened to be at Ashina Rangan's headquarters as well, and Ashina Rangan had him meet with Emperor Yang. Pei then suggested to Emperor Yang that Goguryeo should be subjugated—pointing out that Goguryeo territory was formerly ruled by Han Dynasty and Jin Dynasty. Emperor Yang was enticed, and he issued an edict, to be taken back to Goguryeo's king Gao Yuan (King Yeongyang), in which he ordered King Yeongyang to visit him at Zhuo Commandery (涿郡, roughly modern Beijing) in 611 or face consequences. King Yeongyang, in fear, began to prepare for war, as did Emperor Yang, believing that conquest would be easy. (The subsequent campaigns against Goguryeo in 612, 613, and 614, particularly the one in 612, however, was disastrous for Sui, as great human and material costs were expended with only minimal territorial gains, leading eventually to Sui's downfall.) In 611, after Western Tujue's Chuluo Khan Ashina Daman similarly refused to visit Emperor Yang, Pei suggested forming an alliance with Ashina Daman's subordinate Ashina Shekui, who had been requesting to marry a Sui princess. Emperor Yang agreed, and subsequently, Ashina Shekui attacked Ashina Daman, defeating him and forcing him to flee to Gaochang. Emperor Yang then sent Pei to Gaochang to persuade Ashina Daman to come to Sui, and Ashina Daman did; he subsequently stayed in China and did not return to his own land. Emperor Yang, pleased with this development, awarded Pei with a sable coat and jewels that Ashina Daman offered as tribute. Meanwhile, another strategy offered by Pei to keep the Eastern Turks divided and controlled backfired. Pei had become apprehensive that Ashina Rangan's son and successor the Shibi Khan was becoming strong and difficult to control and had therefore suggested that Emperor Yang offer to marry a princess to the khan's brother Ashina Chiji (阿史那叱吉). Ashina Chiji, in fear, declined.