The Suiyuan campaign was an attempt by the Inner Mongolian Army and Grand Han Righteous Army, two forces founded and supported by Imperial Japan, to take control of the Suiyuan province from the Republic of China. The attempted invasion occurred in 1936, shortly before the Second Sino-Japanese War. The Japanese government denied taking part in the operation, but the Inner Mongolians and the other collaborationist Chinese troops received air support from Japanese planes and were assisted by the Imperial Japanese Army. The entire operation was overseen by Japanese staff officers. The campaign was unsuccessful, mostly due to lack of training and low morale among the Mongolians and other collaborators. The defense of Suiyuan, one of the first major successes of China's National Revolutionary Army over Japanese-supported forces, greatly improved Chinese morale.