By your logic, most Irish-Americans were "British-American", most Polish-Americans and Jewish-Americans were "Austro-Hungarian-Americans" and "Imperial Russian-Americans". The forumla is [ethnicity]-American, though it's debateable whether to include him as an American at all unless we have source to show that he considered himelf one. Your suggestion regarding the Kingdom is quite funny, given that he was 62 when it was formed. I don't see what's unacceptable about the current phrasing to be honest.