Complex sentence: He and his henchmen try to uncover his attackers'identity whilst simultaneously trying not to worry their American visitors, rightly realising if the Americans think he's not in full control of his affairs they won't go into partnership with him.
Split into simpler sentences: He and his henchmen try to uncover his attackers'identity whilst simultaneously trying not to worry their American visitors. Harold rightly realises if the Americans think he's not in full control of his affairs, they won't go into partnership with him.