Complex sentence: Even if this was a semi-conservative party, He became friend of the socialist syndicate leader Natale Gaiba, killed by fascist blackshirts in 1923: this and many other episodes rooted in him a big contempt against Fascism.
Split into simpler sentences: Even if this was a semi-conservative party, he became friends of the socialist syndicate leader Natale Gaiba, who would be killed by fascist blackshirts in 1923. This and many other episodes rooted in him a big contempt against Fascism.