[ankalagon]

Well, in this case, it was clear that the choice was between Communism and military totalitarist regime/falangism/Fascism:

There was a failed coup by the PSOE and left-leaning political groups in 1934: https://en.wikipedia.org/wiki/Revolution_of_1934

They failed and the next two years were a sequence of minor scale violent events that ended in a war in 1936. Of course, the coup by the military forces is not justified, but the caotic situation made them choose what they thought was the "lesser of two evils".