On 1 November 1910, restive workers in the city of Barcelona formed the Confederación Nacional del Trabajo, an organisation that would leave a significant mark on Spanish politics in the following decades.
Traditionally, employers in Barcelona were hostile to even moderate trade unions, and the state was just as unpopular with labourers after it had called up workers to a resented colonial war in Morocco in 1909. The workers wanted a strong and combative representative organisation, and so the CNT came into being.
It rejected the reformism of its rival, socialist-affiliated UGT, and its aggressive rhetoric and actions led to several periods of clandestinity. After becoming the most powerful labour force in Catalonia, Aragon, Valencia and Andalucía, the open conflict it engaged in during 1919 with Barcelona industrialists and police led to its prohibition during the Primo de Rivera dictatorship.
After the creation of the Second Republic in 1931, the CNT rose again, once more jostling for position with the Socialists and their UGT, and also riven with internal contradictions.
The internal balance tilted in favour of the radical Federación Anarquista Ibérica faction, who eschewed any form of collaboration with even a left-wing republican government, when moderates who had called for compromise and government participation were forced out.
When Franco's forces rose up against the Spanish state in 1936, the CNT played a key role in the defence of several cities that stayed in Republican hands, also taking part in large-scale experiments in collectivisation and workers' self-management.
The CNT was involved in the 1937 May Days clashes between anarchists and Trotskyists on one side and socialists and communists on the other in Barcelona. The end result was CNT concessions in the direction of a more disciplined and centralised anti-Franco front, which were nevertheless not enough to prevent the General's victory in 1939. The proscription of the CNT and persecution of its members followed.
Despite being legalised again after Franco's death in 1975, it has so far failed to regain its former strength and is now dwarfed by the Workers Commissions and UGT.
It currently claims to have 50,000 members.