The leaders of the CNT and FAI themselves declared after the uprising of May 1937: “Had we wished, we could have seized power at any time, because all the forces were on our side, but we did not want any dictatorship,” etc., etc. What the Anarchist servitors of the bourgeoisie did or did not want is in the long run a secondary issue. They did, however, admit that the insurrectionary proletariat was strong enough to have conquered power. Had it possessed a revolutionary and not a treacherous leadership, it would have purged the state apparatus of all the Azañas, instituted the power of the soviets, given the land to the peasants, the mills and factories to the workers – and the Spanish revolution would have become socialist and unconquerable.

But because there was no revolutionary party in Spain, and because there was instead a multitude of reactionaries imagining themselves as Socialists and Anarchists, they succeeded under the label of the Popular Front in strangling the socialist revolution and assuring Franco’s victory.

On the Causes of the Defeat of the Spanish Revolution

Funny enough, he advocated the popular front in Germany, but the Trotskyist line was always the necessity of the revolution as part of a struggle against fascism.

The policy of a united front of the workers against fascism flows from this situation. It opens up tremendous possibilities to the Communist Party. A condition for success, however, is the rejection of the theory and practice of "social fascism", the harm of which becomes a positive measure under the present circumstances.

The social crisis will inevitably produce deep cleavages within the social democracy. The radicalization of the masses will affect the social democrats. We will inevitably have to make agreements with various social-democratic organizations and factions against fascism, putting definite conditions in this connection to the leaders, before the eyes of the masses.... We must return from the empty official phrase about the united front to the policy of the united front as it was formulated by Lenin and always applied by the Bolsheviks in 1917.

Fascism: What it is and How to Fight it