When discussing Spain and Yugoslavia, you have to add in the fact that both of those countries had a population of people who had some military training and backing, had other countries supporting the different sides, and there was no powerful overarching government that could overpower one side or the other in the short run.
Can you imagine Russia, the EU, or China trying to support the leftists with weapons or manpower in this conflict?
No, I agree that doesn't seem likely. But I can imagine the government off to the side and unable to quell violence between political factions that is sufficient to cause significant chaos. And this perhaps leading to a collapse a la the Soviet Union.