Theocratic Mongolian monarchy under the Jebtsundamba Khutuktu (Bogd Khan), declared independent of Qing China in 1911; briefly ended by Chinese re-occupation in 1919, restored 1921 with Soviet-backed revolutionary support, and finally dissolved into a communist republic in 1924.
The Bogd Khan (nominal head of state) died in 1924; the revolutionary government then abolished the monarchy and proclaimed the Mongolian People's Republic on 26 November 1924.
Standard modern academic history covering the Bogd Khanate, the 1921 revolution, and the transition to the Mongolian People's Republic.