He rejected reformism, in favor of "continuous attack" against institutions of capitalism and the state, and opposed any form of formal organization, which he saw as inherently corrupting and hierarchical.

In 1888, he went on a lecture tour in towns throughout Piedmont and led a series of strike actions by Piedmontese workers in both Turin and Vercelli, increasing support for the anarchist movement and the POI.

[13] There he collaborated with the French anarchist geographer Élisée Reclus in the preparation of his Nouvelle Geographie Universalle and organised a students' demonstration at the University of Geneva, in honor of the Haymarket martyrs.

[17] Back in Italy, he immediately continued his radical activities,[18] embarking on a speaking tour of Tuscany,[19] with the aim of fomenting an uprising on International Workers' Day of 1891.

[21] In opposition to the social democrats, led by Lombard lawyer Filippo Turati, an alliance was formed by the anarchists and the workerists, who both opposed political participation.

[24] The congress proved that Galleani's agitational campaign had ultimately failed to gain a mass following among the workers, leading to many Italian anarchists becoming disillusioned with the labor movement, which came under the direction of the PSI.

[34] Galleani settled in Paterson, New Jersey,[35] a hub for Piedmontese immigrant silk weavers and dyers,[36] where he took up editing the Italian anarchist newspaper La Questione Sociale.

[41] With these new comrades, on 6 June 1903,[42] he launched Cronaca Sovversiva, which rapidly became the most influential Italian anarchist periodical in North America,[43] receiving worldwide distribution.

[44] Through this new publication, in 1905 he published the bomb-making manual La Salute è in voi!,[45] in which he supplied to his readers the formula for making nitroglycerine, compiled by a friend and explosives expert, Professor Ettore Molinari.

[40] He returned to Barre, where he once again resumed giving fiery speeches and writing hundreds of articles for his newspaper, quickly becoming a leading voice in the Italian American anarchist movement.

[50] He even openly broke with the anarcho-syndicalist Carlo Tresca over the latter's cooperation with the Industrial Workers of the World, causing a rift between their followers that undermined the Italian American anarchist movement's cohesion.

[51] Galleani gained many militant and highly devoted followers, known as the Galleanisti,[52] who likewise rejected all formal organization and developed markedly extremist tendencies.

"[58] In response to the Selective Service Act of 1917 being passed into law, he urged his followers to refuse registration and go into hiding,[59] with he and many of his comrades moving to a cabin in the woods near Taunton, Massachusetts.

[75] Galleani's conception of anarchist communism combined the insurrectionary anarchism expounded by German individualist Max Stirner with the mutual aid advocated by Russian communist Peter Kropotkin.

He defended the principles of revolutionary spontaneity, autonomy, diversity, self-determination and direct action,[76] and advocated for the violent overthrow of the state and capitalism through propaganda of the deed.

"[83] But he also rejected prefigurative politics, such as that advocated by anarcho-syndicalists, as he believed that people themselves would instinctively understand how to live as a free and equal society once the state and capitalism were overthrown.

[87] In the political repression that followed, many of the Galleanisti were arrested, including Italian American anarchists Nicola Sacco and Bartolomeo Vanzetti, who were executed despite the lack of evidence against them.

[89] During the 1930s, the Romanian American anarchist Marcus Graham attempted to revive the Galleanist movement with the San Francisco-based newspaper Man!,[90] but its efforts were unsuccessful and the paper was shut down in 1939.