I did quite a bit of research and do not see any way for me to control a Google group to prevent any country from joining. I am wondering if this is some Google policy (or country Internet policy) that is in force which I cannot override. See https://techcrunch.com/2010/04/19/google-censorship/ and https://onimap.citizenlab.org/filtering-pol.html. What doesn't make sense is that you can see the posts, just not join the membership, which is a very odd type of censorship indeed.

Rob, CJ, krasw - So I can investigate further can you please reply privately contact me and let me know where you are located when trying to join? Are you a member of another (US based) Google Group which might offer a clue?

Thanks, John