her regent, but until the end of his reign, she has decision-making power on most events in the governmental and border matters. Toward the end of Gaozong's life, Wu began engaging a number of mid-level officials who had literary talent, including Yuan Wanqing (), Liu Yizhi, Fan Lübing, Miao Chuke (苗楚客), Zhou Simao (周思茂), and Han Chubin (韓楚賓), to write a number of works on her behalf, including the Biographies of Notable Women (列女傳), Guidelines for Imperial Subjects (臣軌), and New Teachings for Official Staff Members (百僚新誡). Collectively, they became known as the "North Gate Scholars" (北門學士), because they served inside the palace, which was to the north of the imperial government buildings, and Empress Wu sought advice from them to divert the powers of the chancellors: They thus act as a secret secretariat, "to process for the empress memorials addressed to the throne, and to make decisions on the policy which were properly the functions of the chancellors". (The modern Chinese historian Bo Yang suggested that Emperor Gaozong's illnesses may be the result of long-term poisoning by Empress Wu, because of his long and debilitating illness, he often left his responsibilities to Empress Wu, or had to rely on her when himself wanted to address political issues, but did not provide evidence of how the poisoning took place.) Also in 675, Li Hong the Crown Prince died suddenly—with traditional historians largely attributing his death to poisoning by Empress Wu, due to her anger that he tried to curb her power grab and had shown sympathy to his two older sisters born of Consort Xiao—Princesses Yiyang and Gao'an. Emperor Gaozong and Empress Wu, in grief, posthumously honored Li Hong as an emperor, and he created Empress Wu's second son, Li Xian the Prince of Yong, crown prince. Along with the war with Silla, some resistance of Goguryeo people continued to plague Tang rule there. In 676, Xue Rengui crossed the Yellow Sea to fight against Silla. However, Silla navy expelled Tang forces on the coast of western Silla. Emperor Gaozong and Empress Wu order withdrawal of Tang forces from the Korean Peninsula entirely and moved the Protectorate General to Pacify the East to Liaodong (遼東, in modern Liaoyang, Liaoning) and the commandant of Xiongjin (), who governed the former Baekje territory at Sabi, to Geonan (建安, in modern Yingkou, Liaoning), allowing Silla eventually to expel Tang out of the Korean