What’s your understanding of the entire situation? Are you suggesting that it was going well until the Communists backstabbed the Anarchists? Taking a real, materialist analysis of the situation is necessary. Historically, Communists and Anarchists have had uneasy alliances until differences in organizational theory lead to friction and then conflict.
I don’t know how the war would have gone if those events hadn’t taken place, but it seems to have undermined the strength of the popular front. And from what I’ve read the anarchists were sufficiently organized. The type of Anarchism popular amongst the Spanish was a syndicalist strain very different from the hyper-individualism people expect from anarchists today.
Why do you think it happened? You implied the fighting was one-sided and a betrayal.