A las Barricadas
"The Confederation" referred to in the final stanza is the anarcho-syndicalist CNT ( — "National Confederation of Labor" ) , which at the time was the largest labour union and main anarchist organisation in Spain , and a major force opposing Francisco Franco's military coup against the Spanish Republic from 1936 to 1939 . 
<triplet> CNT <subj> labour union <obj> instance of