 In spring 668, they further marched east and captured Goguryeo's major northeastern city Buyeo (, in modern Siping, Jilin), and Xue was described to have marched to the sea (probably Sea of Japan) and taking some 40 cities in Goguryeo's northeastern territories, before marching southwest to rendezvous with the supreme commander of the entire operation, Li Ji, at Pyongyang.After Pyongyang fell later in 668, thus ending Goguryeo, Emperor Gaozong ordered that Goguryeo territory be annexed into Tang territory and that a protector general (known as the Protectorate General to Pacify the East) by established at Pyongyang, with Xue appointed as the protector general to defend Pyongyang, along with the general Liu Rengui.Emperor Gaozong created him the Duke of Pingyang.