You could say it's the natural conclusion of any system that consolidates power so much that a small number of people can take over the power in the country, bypassing (or abusing) the current system of power.

Doesn't really matter if this happens because capitalism unifies the power in the hands of a few oligarchs, or if it's socialsm that unifies the power in the hands of a few top-ranking officials or if it's the military that blindly follows a hand full of generals.

Whenever you have a system that doesn't balance itself, where power gets accumulated over time, then the natural conclusion will be some kind of dictatorship, and fascism is a popular variant of that.