Prior to World War II, Mongnai State (Burmese, Mo-Ne) was one of the largest and the most important of the States in the Eastern subdivision of the Southern Shan States. The early history of Mong Nai State is buried in obscurity. The town has been several times burnt, as it has always been the centre of disturbances in the Southern Shan States, and all records have perished in the various fires.
The original city, according to Burmese accounts, was founded in the year 24 of Religion (519 BC) by Sao Hkio, who was the first of a line of independent Chiefs. In about 1223 AD, Mong Nai was conquered by Sam Long Hpa of the Northern Shan Empire and became tributary to Se Lan, the old Mong Mi line of Saophas (Sawbwas) was then put in charge of the State.