what's the difference between was and had been?

That is what is known as a relative tense. "Had been" is relative to "was." So the author is talking about someone in past. Sayings was or had been means that in that time in the past, the person was a fascist, or at some time even further in the past, had been a fascist--but the author does not positively know if he still was a fascist at that absolute time in the past.

Perhaps this Wikipedia article will help you to understand it. "Was" is an absolute past, one can know when that was. "Had been" is a relative past--it relates to the absolute past, and occurs before that absolute past. In French, this is what is known as the anterior past tense--the past, before the past.

Maybe this will help:

Tuesday he was an hour late; he had been late on Monday, too, but i don't know by how long.

Tuesday is the absolute past, Monday is the past before the past, realtive to Tuesday, so it is the relative past.

Set meant "anti-fascist".

This portion of the Wikipedia article is misleading. Would is NOT the past tense of will.

English uses absolute tense. For example, if John told someone "I will go to the party." but doesn't show up, that person would report his words as "John said that he would come." Because the event took place in the past, all verbs must be in the past tense. (Would is the past tense of will.) The phrase "John said that he will come" means something different: That the time of his expected arrival is in the absolute future, later than the time of reporting it.

If John tells someone "I will go to the party." but hasn't yet shown up [the party is still in progress] the report of speech could still be,

"John said that he would come."

The 'would' has no past time meaning, hence it is not a past tense.

A speaker could certainly choose to report the speech as,

"John said that he will come."

These backshifts [will to would/may to might/can to could/...] are markers of direct versus reported/indirect speech. They are NOT indicators of tense/time.

thank you so much!

thank you!