The Silla kingdom had formed a military alliance with the Tang empire under Emperor Gaozong's reign. When Goguryeo and Baekje attacked Silla from the north and west respectively, Queen Seondeok of Silla had sent an emissary to the Tang empire to desperately request military assistance. In 650, Emperor Gaozong received a poem, written by Queen Seondeok, from the princely emissary Kim Chunchu (who would later accede the Silla throne as King Muyeol). Baekje had allied with Yamato Wa in 653. Even though Baekje was allied with Goguryeo, the Han River valley separated the two states and was a hindrance in coming to each other's aid in time of war. King Muyeol assumed the Silla throne in 654. Between 655 and 659, the border of Silla was harassed by Baekje and Goguryeo; Silla therefore requested a