In 237, Cao Rui once again considered attacking Liaodong, angered by reports that Gongsun had repeatedly defamed him. He commissioned Guanqiu Jian to prepare for an attack, and then ordered Gongsun to come to Luoyang for an official visit. Gongsun refused and instead declared independence. Guanqiu attacked him, but was stopped by torrential rains. Gongsun then declared himself the Prince of Yan and entered into alliances with the Xianbei tribes to harass Cao Wei's borders.
