Chahar Province
After Japan seized Manchuria through the Mukden Incident in 1931, Beiping was threatened by steady Japanese encroachment into northern China. The Tanggu Truce of 1933 gave control of the Great Wall to the Japanese and imposed a 100-km demilitarized zone south of the wall. This deprived Beiping of its northern defenses. The secret He-Umezu Agreement of May 1935 required the Chinese government to remove Central Army units from Hebei Province and suppress anti-Japanese activities by the Chinese public. The Qin-Doihara Agreement of June 1935 compelled the Nationalist 29th Army, a former unit of Feng Yuxiang's "Guominjun" that fought the Japanese in defense of the Great Wall, to evacuate from Chahar Province. This army was relocated and confined to an area south of the Beiping near Nanyuan. In November 1935, the Japanese created a puppet regime based in Tongzhou called the East Hebei Autonomous Council, which declared its independence from the Republic of China and controlled 22 counties east of Beiping, including Tongzhou and Pinggu in modern-day Beijing Municipality.