By 1940 China was engaged in World War II fighting against the Japanese invasion and Britain was involved in the war against Germany. Hsu chose to leave Britain to return to his homeland of China where he was appointed as Professor at Peking University.
Sa pamamagitan ng 1,940 Tsina ay pansin sa World War II labanan laban sa Japanese paglusob at Britain ay kasangkot sa digmaan laban sa Germany. Hsu pinili upang umalis sa Britain upang bumalik sa kanyang tinubuang-bayan ng Tsina na kung saan siya ay hinirang bilang Propesor sa Peyping University.