Present-day eastern Inner Mongolia, then part of Manchuria, came under the control of the Japanese puppet state Manchukuo in 1931, and was administered thus until the end of the war in 1945.
In 1937, open war broke out between China and Japan. On December 8th, 1937, Mongolian Prince Teh Wang declared the independence of Inner Mongolia (except the parts already in Manchukuo) as Mengkiang or Mengkukuo and signed close agreements with Manchukuo and Japan, thereby turning Inner Mongolia to a puppet of the Japanese Empire. The capital was established at Chan Pei, near Kalgan, with the puppet government's control extending around Hohhot. In August 1945, Mengkiang was taken by Soviet-backed communist rebels.