You don't control a whole country, you have on city (or now "region"). Any it's made so that Sims only move to your city if you provide everything. They wouldn't move to a new city where there is nothing, no schools, no fire department. I think that's close to the real world. If there is a new town or new part of a town to be build, no one would move there unless some people in charge decide to provide basic services.