Help me find a book I forgot the name of

I need help finding this science fiction book set on earth. All I can remember about it was that there is a town or city that no one can enter but the original inhabitants. Other countries are trying to figure out how to get in and why it's happening in the first place and there may have been aliens involved. It's been so long, I'm sorry if this wasn't enough detail. I just recall the other countries getting frustrated at not being able to enter freely, and it wasn't under the dome or wayward pines.