The War of the Insane or the Madman's War (Guerre du Fou) was a Hmong revolt against taxation in the French colonial administration in Indochina lasting from 1918 to 1921. Pa Chay Vue, the leader of the revolt, regularly climbed trees to receive military orders from heaven. The French granted the Hmong a special status in 1920, effectively ending the conflict.
The rebellion, called "Rog Paj Cai" by the Hmong nationalists and "Rog Phim Npab" by Hmong who sided with the French, was a self-initiated and self-sustaining movement; all the guns were Hmong-designed and manufactured flintlocks (a bit different from the traditional western flintlock gun). The gunpowder was also of a Hmong sort (salt peter, charcoal, and guano was used similar to western black powder, but shavings from a type of tree were added to increase the explositivity). The Hmong won battle after battle for the majority of the rebellion; the French were surprised and did not know how to fight in the jungles nor did they know how to fight a near invisible army. France was also heavily involved in World War I in Europe, and resorted to using 50% French and 50% native Vietnamese, Lao, and Tai, and Hmong soldiers, who all had little desire to fight the rebel Hmong forces.
One particular weapon that especially scared the French army was the Hmong cannon, made with the trunk of a tree, and packed with metal pieces from pots, and a lot of Hmong gunpowder. This cannon was designed by Kuab Chav, and is said to have weighed over 200 lbs, such that only one man named Lwv was able to carry it. As the French army came up the mountainous trails, the cannon would spray the metal shards at the French army, sending them into hiding while wounding and killing many of them. They never knew what it was because they assumed the Hmong did not have the technology to build such a weapon.
The French morale was also weakened because of rumors that Pa Chay's army was protected by magic. As the French Army chased the Hmong army through the mountainous passes and ravines, they never saw any dead Hmong soldiers. The reason was that Pa Chay had commanded his men to never leave anyone behind, and to cover up the blood as quickly as possible. This gave the illusion to the French that Pa Chay's army was indeed invincible.
Kao Mee, a sister of Pa Chay, also played an important role. She carried a white flag made of hemp, which she used to deflect bullets. She is said to have been a righteous virgin, which is why the Heavens allowed her to have such miraculous powers. She led the army into many successes in battle.
At its height, the rebellion encompassed 40,000 square kilometres of Indochina, from Điện Biên Phủ in Tonkin to Nam Ou in Luang Prabang, and from Muong Cha north of Vientiane to Sam Neua in Laos. As World War I came to an end, the French reinforcements began to outnumber the rebels, and their firepower overpowered the Hmong. They also learned from certain Hmong informants such as Lauj Kiab Toom that the Hmong gunpowder did not work well when wet, so they attacked especially during the monsoon season. The Hmong believed their defeats were temporary, caused by violations of the Oath to Heaven by some of the soldiers, and despite these defeats, there was still strong support from the populace.