Need to start somewhere. Logistically, it's to hard to do "the entire world" as a single step.
On the other end, just a single town or county is to small. To much interaction with outside groups. Start one country at a time and build out from there. Even one state is probably to small, there's lots of cross state interactions relative to their size.
Eventually (hopefully) we can reach the rest of the world over time then, and there will not be any outside group left to interact with. Or, will there......