Inactivity
Worlds with Predetermined Countries are not set up to resign users. The idea was that each player gets one country and then that country is permanently taken. (I may reverse that and turn the normal 31 days of inactivity rule, though.)
Players joining and never playing has always been a big frustration in the game, though. So, in all worlds, I think I'm going to change the game so that a player must visit the game at least one time in the first two days it begins (or return at least once in the next two days after joining). If not, the country will be resigned automatically. Then, the normal 31 days of inactivity rule takes effect.