HAVANA—On the sidelines of the 24th International Meeting of Communist and Workers’ Parties, held in Havana in early August, representatives of the Communist Party USA, the Communist Party of Britain, and the Communist Party of Australia sat down together and emerged with a three-nation demand: Scrap the AUKUS nuclear submarine pact. The trilateral meeting, the second of its kind since the three parties first denounced AUKUS shortly after it was…