By autumn 1938 the most tangible political reality in the centre–south zone was the massive hostility developing apace between socialists and communists. This would eventually lead to violent confrontations which destabilised the entire zone – and with it the loyalist war effort. Although the struggle between socialists and communists was being waged across the whole range of political organisations and at all levels of government administration in the Republican zone, the tension was particularly acute in the unified youth organisation. There, it was reaching the proportions of an internal civil war.

This conflict set the national leadership of the JSU — which was entirely loyal to PCE discipline and Popular Frontist policies - against the resurgent old-guard young socialists, many of whom had retained their caballerista faith. The latter, having hoist aloft the banner of anti-stalinism in the drive to re-establish an independent socialist youth organisation, were gathering about them an everincreasing following from the socialist rank and file. By the middle of August 1938 the socialist left was openly advocating breaking up the JSU. This was first broached publicly by the ASM's secretary, the Caballerista, Enrique de Francisco, at a meeting of socialist trade unionists in Madrid on 21 August.