If every system has what it will become inside it already then what decides if liberal economies become socialist or fascist?

At risk of answering my own question, I'm under the impression that fascism is a reaction to rising socialism in a given economy. I've only just begun reading "Blackshirts and Reds" by Michael Parenti but I want to hear from other marxists about this.

Are there other books or writings on the topic you recommend? Am I oversimplifying?