It started when supporters of the Phu Mi Bun religious movement initiated an armed rebellion against French Indochina and Siam, aiming at installing their leader, sorcerer Ong Keo, as ruler of the world.

Larger tribal groups often raided weaker tribes abducting people and selling them into slavery at the trading hub of Champasak, while themselves falling prey to Khmer, Lao and Siamese slavers.

[2] In late March 1901, the French Commissioner of Saravane formed a small band of militiamen in order to investigate the popular gatherings organised by sorcerer Ong Keo on the Phou Kat mountain.

Ong Keo had managed to gain a large following among the Alak, Sedang, Loven and Nha-heun tribals who venerated him as a proto-Bodhisattva, creating the millenarian Phu Mi Bun (Ruler of Justice) movement.

[2][1][4] A prophecy then began circulating in Northeast Siam, various prophets claimed that a great catastrophe was going to take place in May 1901, while Phu Mi Bun would emerge as the ruler of the world.

On 28 March, Ong Man's troops raided Khemmarat in Siam, executing two officials, abducting the governor while also burning and looting the town.

On 3 April 1902, Siamese troops ambushed a rebel column outside Ubon, killing 300 and capturing 400 militants, the guerrillas that managed to survive the encounter fled to Laos.

Renewed French operations forced Ong Keo to surrender; however, he soon fled to Siam only to return to Laos and resume his struggle in the Bolovens Plateau.