The conflict arose from a millenarian cult led by Antônio Conselheiro, who began attracting attention around 1874 by preaching spiritual salvation to the poor population of the sertão, a region which suffered from severe droughts.

Antônio Conselheiro and his followers were branded as "monarchists" by the press, with the authorities seeing the settlement as a threat to the recently proclaimed Brazilian Republic, which was still in process of consolidating itself.

The conflict came to a brutal end in October 1897, when the fourth and final expedition, led by General Arthur Oscar, with a large fraction of the Brazilian Army, was deployed to bombard and overrun the settlement, raze it and slaughter nearly all its inhabitants.

The conflict had its origins in the former settlement of Canudos (named Belo Monte by its inhabitants, meaning "Beautiful Hill" in Portuguese) in the semi-arid backcountry (or sertão) of Bahia.

Within two years, as the religious community prospered, Conselheiro convinced several thousand followers to join him,[8] eventually making it the second-largest urban center in Bahia at the time.

[9] Determining what exactly happened in the war is problematic, as the two main historical source groups consist of military chronicles (written to justify the army's actions) and far-from-impartial journalistic reports.

[10] According to Peter Robb, "[t]he foreign correspondents who covered what was soon being called the War of Canudos, as if it were a conflict between nations rather than the extermination of a tiny community within a single country, were nearly all embedded with the army of the Brazilian republic.

[3] Hearing of this plan, the judge responded by requesting police forces from the state governor, Luis Viana, claiming an imminent "invasion" of his town by Conselheiro and his followers.

[3] Viana recounts that he had been informed by Leoni of "rumors which were current, and which were more or less well-founded, to the effect that the flourishing city in question [Juazeiro] was to be assaulted within a few days by Antônio Conselheiro’s followers.

"[3] While the troops were initially dispatched for the sole purpose of preventing the assault, Leoni managed to convince their commander Pires Ferreira to march on Canudos.

[3] Estimates of the number of Conselheiristas that engaged in the battle varied anywhere from 1,000 to 3,000 men, and accounts reported that they were armed with "old muskets, pikes, scythes, long poles, and implements of the land.

The media (i.e. newspapers) played an essential role in escalating the conflict, spreading rumors that rather than being a local and unsophisticated uprising, the Conselheiristas were allied with other monarchists scheming to launch a "restoration" of the monarchy.

[12] The settlement was fiercely defended by a band of 500 armed men, shouting praises to Antônio Conselheiro and the monarchy, and the attacking force faced problems similar to the first expedition.

[12] The defeat of the Pires Ferreira campaign produced sensationalist media reports about the ferocity and fanaticism of Canudos' inhabitants, which provoked an outcry and calls for reprisals against the settlement.

[12] The attack on the Conselheiristas began on January 18, and led to the death of 115 Canudenses with minimal losses on the army's side,[3] which had some initial success with artillery against the villagers' trenches.

[12] Running short of ammunition, food and water, and with the rebels continuing to fight despite heavy losses, the Republican soldiers retreated to nearby Monte Santo to await reinforcements.

[12][3] Canudenses celebrated their victory against the expedition in a particularly destructive way;[3] burning ranches and farm buildings, creating a ring of scorched earth within a radius of seven miles of Canudos.

[16] In Rio de Janeiro and São Paulo, the country’s largest cities, where monarchism was very unpopular, demonstrations in the streets turned into riots and four monarchist newspaper offices were destroyed, and the owner of one lynched.

[12] Machine guns and large artillery pieces, such as mortars and howitzers, including a powerful Whitworth 32, nicknamed Matadeira (Killer), went with the 3,000-man force, and had to be hauled with enormous effort through the unforgiving roadless landscape.

[3] They were hindered by the fact that the rebels now possessed "some of the most advanced weapons of the time" (repeating rifles "like the Austrian Mannlicher and the Belgian Comblains"), abandoned by fleeing republican troops.

[3] Before Canudos was burned down and dynamited, Conselheiro's body was exhumed, the head was removed, and it was "displayed on a pike" to be "held high at the front of a military parade for all to see.

"The desperately poor peasants" had been fighting by themselves without help, and had "no connection whatsoever with real monarchists – white, upper-class urbanites, who were horrified at the very thought of associating with such a 'riffraff' of 'fanatics'"[4] The war "turned out to have been an inglorious massacre of destitute wretches", in which the military had made a "common practice – approved by the commanders" – of tying up prisoners and beheading them in public.