Complex sentence: Unusually for a revolutionary his funeral was a state event in his native Greece which circumstance is explained by his friendship from the 1930s with Andreas Papandreou who had been a Trotskyist in his youth.
Split into simpler sentences: Unusually for a revolutionary, his funeral was a state event in his native Greece. This is explained by his friendship from the 1930s with Andreas Papandreou who had been a Trotskyist in his youth.