The various left groups were busy infighting, as happens so often throughout the history of conflicts, and ultimately left themselves vulnerable to the right wing Franco's regime. History ultimately has ended up well for Spain (even history absolved them for sympathizing with Hitler) and the issue has long been put to rest.
Anytime you have groups so divided on issues. It is going to cause major problems. It creates a dysfunction to where people can't get anything accomplished. Which means, these power struggles were most like the cause of why they loss the Spanish Civil War. I am sure there were other factors, but we are always stronger together, rather than divided.
Yes, these power struggles were the main thing that set off the spanish civil war. I think that the two sides in this were very mad at each other, and that the only way to settle it was to make war and just fight it out to see who won.
The Republican loss in the Spanish Civil War had a variety of causes. Not least among these were the disagreements between leftist factions. However, to call these disagreements the "main" cause of Republican defeat is to overstate the case. A more nuanced picture would include the effects of the shifting opinions of the populace, as well as the logistical problems faced by Republican forces.
No, the power struggles between the various factions on the Left were not the main cause of the Republican loss in the Spanish Civil War, because the main cause was that Franco was simply too popular. Franco had a cult of personality about it, so people who did not know what to believe sided with the opposition.