Complex sentence: Because of his political sympathies, Menjou came into conflict with (by American standards) radical left-wing actress Katharine Hepburn, with whom he appeared in the films "Stage Door" and "State of the Union", the latter also starring Spencer Tracy.
Split into simpler sentences: Because of his political sympathies, Menjou came into conflict with actress Katharine Hepburn, who was considered a radical left-winger by American standards. He he appeared wiht her in the films "Stage Door" and "State of the Union", the latter also starring Spencer Tracy.