Despite for much of the 20th Century being known as the “Switzerland of Latin America” for its peaceable democratic climate rooted in arguably one of the world’s first welfare states under the “radical liberal” anticlerical President José Batlle y Ordóñez from 1910, the small South American republic of Uruguay also produced the continent’s most combative armed anarchist movement. With remarkable political, strategic, and tactical sophistication and verve, the majority of the country’s anarchists waged war on the state as it declined into dictatorship in the period of continental mass-murdering fascist regression in the late 1960s through mid-1970s. But beyond taking up arms on a more ethically grounded basis than their better-remembered compatriots such as the Tupamaros who also engaged in armed struggle, the anarchists built one of the largest fighting mass working class movements of the post-Spanish Revolution era – against the servile reformism of the Uruguayan Communist Party, the continent’s fourth-largest – with an anarcho-syndicalist shaped national union centre some 400,000 strong by 1972, roundly refuting the notion that mass-formation anarchism had died on the barricades of Barcelona in 1939. The unique importance of the Uruguayan experience is necessary to stress: it demonstrated the validity of mass-line anarchism within modern industrial societies decades after World War II; it neatly updated Mikhail Bakunin by cleverly articulating between what it termed the “levels” (or “grades”) of the militants and the masses; and it developed an actively engaged political practice that anticipated what in Latin America today is called “social insertion.” That the very existence of this mass-ranked experiment in libertarian communist counter-power has been airbrushed out of history by anarchists as much as by the usual leftist suspects, the Marxists, is a testament to the troubling potency and pragmatism of its ideas. This paper is a partial extract from my forthcoming book In the Shadow of a Hurricane: Global Anarchist Ideological and Organisational Lineages, which took 18 years’ research in 14 languages.