It didn't last because others attacked it.
That is not an unsolvable problem.
It requires democracy and people demanding their governments stop attacking others.
Something Americans are presently incapable of doing.
Sorry. I just mentioned the reason Orwell gave in the book. What he believed. It's not the reason I believe.
I believe that the Spanish civil war was a proxy war between the main belligerents of what became WW2. The anarchists were basically noise. Bugs swatted when they got annoying to the big boys. Spain had had political instability for half a century prior to the outbreak of the war. Even before the outbreak all the Spanish wanted was peace and stability. I doubt most Spanish gave a rats ass who won. By that time they were just sick of revolutions.
It's a similar situation in Syria. Any reasonable home grown rebel force just gets steamrolled. The ideas or ideology, in that war, is pretty much irrelevant. It's more important who your allies are. But your allies will inevitably take over and obliterate your independence. Play along or get exterminated.
That's got nothing to do with ideology. That's purely real politik.