This XenForo 2.1 addon provides Geoblocking capabilities for user registration.
You can set allowed and denied lists for countries based on the IP address a user registers from - and optionally force users from non-approved countries into the moderation queue when registering.
The addon uses the free
Maxmind GeoLite2 downloadable IP database to identify the country associated with the IP address of a registering user.
As an example, a typical use-case...
