The Spanish Civil War - pg. 230

The most likely explanation for Franco's decision not to launch
an immediate assault on Barcelona was pressure from his allies.
Hitler was nervous of British and French reactions after his
Austrian coup and he was not interested in the rapid defeat of the
Republic. Not long before, he had emphasized the need to divert
attention from his expansionist policies in central Europe: 'From
the German point of view we are not one hundred per cent
interested in a Franco victory. What does interest us is a prolongation
of the war in Spain, so that tension in the Mediterranean is increased.'
It has even been suggested, but not proved, that the German
government supplied the Republic with arms.