Initially based in Donostia, in the Basque Country, the group was forced to flee to Zaragoza after its plot to assassinate King Alfonso XIII was uncovered.
With guns acquired from Basque anarchists, the group carried out an armed robbery of a paymaster, which financed the further acquisition of weapons and the clandestine activities of the Confederación Nacional del Trabajo (CNT).
The group then fell into political and tactical disagreements, with one part, led by Buenaventura Durruti and Francisco Ascaso, moving to Barcelona and founding Los Solidarios.
In the wake of the 1917 Spanish general strike, anarchists in the Basque Country first began carrying out propaganda work in the region, which laid the groundwork for the rise of anarcho-syndicalism.
By the time of the Second Congress of the Confederación Nacional del Trabajo (English: National Confederation of Labour; CNT), which took place in 1919, organised anarchist activity was spreading throughout the Basque Country.
[4] In Donostia, local anarchists led by Moisés Ruiz organised Aragonese and Castilian migrant workers who had been brought to the city to build the Kursaal Casino.
He was soon joined by anarchists from Zaragoza and Logroño, including Cristóbal Albadetrecu, Marcelino del Campo, Víctor Elizondo, Clemente Mangado, Inocencio Pina, José Ruiz and Gregorio Suberviola.
In the Basque Country, lieutenant colonel Fernando González Regueral was appointed as governor, and he immediately ordered mass arrests of trade union activists.
Inspired by the assassination, Los Justicieros began planning their own attempt against Fernando González Regueral, before learning that King Alfonso XIII intended to attend the opening of the Kursaal Casino.
They found out that, in December 1920, the young militant Francisco Ascaso had been imprisoned and was awaiting a death sentence, having been charged with murdering the editor of the conservative newspaper Heraldo de Aragón.
[13] Upon their return to Zaragoza, the local groups decided to prepare for the eventual formation of an Iberian anarchist federation when conditions made holding a national conference possible.
The CNT had been driven underground and most of its funds had been spent aiding the families of its arrested members, so they were only able to acquire small amounts of cash and a few pistols from local militants; their suppliers quipped that, at that time, "a gun was the best membership card".
[19] Unable to quell the unrest, Manuel Allendesalazar resigned as prime minister and was replaced with Antonio Maura, who was tasked with cracking down on the anti-war and labour movements.
[20] Aiming to destroy the labour movement and win over the Catalan bourgeoisie, Maura imprisoned a large number of union activists, forced chain gangs to maintain the country's roads,[21] and increased the use of assassinations against workers.
[21] King Alfonso XIII wanted a new government that could imitate the fascist regime of Benito Mussolini, but instead, José Sánchez-Guerra moved to reinstate constitutional rights.
[22] While Los Justicieros began to prepare for open conflict, the anarchists' defense lawyer, Eduardo Barriobero, called for mass protests against the trials in order to bide time until the restoration of constitutional rights.
[23] On 19 April, the anarchists began circulating pamphlets calling for a general strike against the trial and organised a political demonstration outside the High Court of Justice of Aragón [es].
Although advised by Domingo himself to stay in Zaragoza,[30] Francisco Ascaso, Durruti, Escartín, Suberviola and del Campo broke from the rest of the group and decided to move to Barcelona.
[1] The actions of Los Justicieros influenced the New Afrikan anarchist Kuwasi Balagoon, who read about their raids and assassinations while in prison and who believed their example could be followed by the Black liberation movement.