The military coup of July 1936 against the progressive, reformist Second Spanish Republic precipitated a movement of popular resistance in which could be glimpsed the revolutionary potential of the social base of Spain's Popular Front (the centre-left electoral coalition victorious at the polls in February 1936). These radical energies would dissipate and the revolutionary attempt fail largely through the internal insufficiencies and inconsistencies of the groups constituting the radical left. But it was nevertheless the driving energy of that popular response which salvaged the reformist Republic, allowing the state to be reconstituted and a three-year war effort to be sustained in desperate conditions. This chapter will suggest some structural and conjunctural reasons why a revolutionary option failed to cohere as a basis for the Republican war effort. In the process it will also seek to indicate how we might go about unpacking the components of ‘Republican disunity’ – often referred to as if it were the product of pure ideological voluntarism and a ‘monolithic’ explanation for defeat.