I think clans are interesting too, but the challenge is that there are not enough users to join groups and countries.
Groups only have about 10-20 users except for medicine and languages. About half of them join countries (so about 1300 users are pirates). So even if we create a clan, most users may not join. (maybe possible in the future if more users join?)
Public groups seem like a good, but private groups may not like or be interested in competing.
So the idea I’m thinking of at the moment is to enhance the national leaderboards as NameLessGo says. It might be interesting to count the ranks of users’ leagues like medals: e.g. UnitedStates: alpha(2) Beta(15) Gamma(30)