High Quality Content by WIKIPEDIA articles! The Defense of the Great Wall (simplified Chinese: traditional Chinese; pinyin: Chángchéng Kàngzhàn) (January 1, 1933 May 31, 1933) was a campaign between the armies of Republic of China and Empire of Japan, which took place before the Second Sino-Japanese War officially commenced in 1937. It is known in Japanese as Operation Nekka (Nekka Sakusen?) and in many English sources as the First Battle of Hopei. During this campaign, Japan successfully captured the Inner Mongolian province of Rehe from the Chinese warlord Zhang Xueliang and annexed it to the new state of Manchukuo, whose southern frontier was thus extended to the Great Wall of China.