"Or they could go totally North Korea and just shut off all the borders and pretend the rest of the world either doesn't exist or must be vastly inferior."
They are already half-way there. Look up how many US citizens have a passport. See how many US politicians are up to speed with events outside the US and just look at the US baseball "World Series". See any non-US teams there?
It's like a lot of places that are big and have an undue influence on their surrounding areas. *Cough* London *Cough*
You don't have to live on an island to be insular.
Biting the hand that feeds IT
