The Sui Empire extended far into Manchuria and spread over the northern half of the Korean peninsula. Almost concurrent with the birth of the Sui Dynasty, the Tujue (Turks) formed a vast nomadic nation comprised of a new and powerful tribal federation of Xianbei nomads that stretched from the Ural Mountains in western Russia across the Mongolian steppes north of China to the northern frontier of Koguryo. Ever watchful of events in China, Koguryo's King Yangwon built ties with the Tujue Empire to confront the Sui Chinese and protect his western territory. The emergence of Sui China and the Mongol Empire had a noticeable impact on the relationships among Korea's Three kingdoms.
In the past, only the Silla-Paekche alliance had been able to keep Koguryo in check. Beginning with the Silla victories in the Han-Imjin River basin, Paekche saw Silla as a mortal enemy. Paekche turned to Koguryo for help (YoJe Dongmaeng) and launched continuous attacks against Silla, a confrontation that presaged a great storm that soon erupted over northeast Asia. Now, only an alliance between Paekche and Koguryo could successfully oppose Silla's growing power. To counter Silla, King Yangwon made an alliance with his southern neighbor, Paekche, who maintained diplomatic ties with the Yamato state in Japan. Unable to conquer his two main rivals unaided, Silla's King Chinp'yong promptly sought an alliance with Emperor Wen's Sui Dynasty and created an east-west alliance to oppose the north-south alliance of the Tujue, Koguryo, Paekche, and Japan.
Facts and Figures :
King Wideok also maintained friendly relations with the Chinese dynasties of Northern Qi and Sui. 567 was also the year that he sent Baekje's first mission to Northern Qi; this may have been facilitated by an improved relationship with Goguryeo.
King Yung-yang personally led 10,000 Mohe soldiers and attacked Liao-xi in 598
King Bo-jang sent a general to relieve the An-shi Fortress in command of the Koguryeo army as well as the 150,000 Mohe soldiers in 645
According to the History of Jin, 150,000 Black-Water Mohe soldiers fought on the side of Koguryeo against the Tang Tai-zongs army at the An-shi Fortress in 645. The Old History of Tang corroborates the fact that 150,000 Mohe soldiers came to rescue the An-shi Fortress, and further states that Tai-zong buried alive the captured Mohe soldiers numbering 3,300 at the Fortress.3
In 654, King Uija of Paekche allied with Koguryo and the Malgals have taken 30 fortress in the north of Silla .the Koguryeo army, together with the Mohe and Paekche soldiers, attacked Silla in 655
King Bo-jang sent a general in command of the Mohe soldiers to attack a Silla castle in 661
2 三國史記 高句麗本紀 長壽王 五十六年(468) 王以靺鞨兵一萬 攻取新羅悉直州
There appear 32 records of Paekche fighting against the Mohe soldiers in the Paekche Pon-ki, and 23 records of Silla fighting against the Mohe soldiers in the Silla Pon-ki.
3 舊唐書 列傳 第一百四十九 上 高麗 靺鞨之衆十五萬來援 安市城 太宗 收靺鞨 三千三百 盡坑之