Fascism and Communism are kissing cousins, both at the same end of the spectrum, and not far from each other, either. As a matter of fact, if you drew Venn diagrams, they would have significant overlap.
Back in the Twenties, Thirties, and Forties of the 20th Century, this was well understood by the observant totalitarians of both ideologies who looked at their “blood enemies” and deduced that their enemies were fertile ground for recruitment, regardless of what their propaganda said.
That’s all one needs to understand. Communism and Fascism can be thought of, from a practical view, of being so close as to be indistinguishable. That is, for all the blather, they are fully formed full-control forms of government.
A government like our constitutional republic not too long ago would have been placed further down the ideological scale towards the opposite end of the ideological spectrum, no government control, or anarchy. We are (were) limited government. But we are sliding towards the full government control section of the ideological spectrum.
The best description I've heard is that they are "two rabid dogs fighting over the same bone."