One option could be to use group hierarchy to nest the city groups within countries. Another option is to take a look at the group types plugins that will allow you to have different categories for groups in effect, you could then add cope to change how WordPress/BuddyPress behaves with those groups.
Thanks.
By the way, what do you mean by
“the group types plugins that will allow you to have different categories for groups “?
Search for “BuddyPress Group Types” you will find a number of plugins that allow you to set a type for a group. but these are typically just starter plugins, you’d have to decide what you are going to do with those types and implement in code.
