>>25007875You choose what region you start in when you enter your name and gender.
After you beat the Champion, you can decide what region you go to next.
However, your badges aren't valid in different regions, so you have to go through the gyms again. And since your badges aren't valid, neither are the abilities granted by them, so no HMs before you beat the requsite gym, and you're not permitted to use pokemon beyond the appropriate level for the gym.
Beat the second Gym in a region? You can now use any pokemon you've caught, even from other regions, as long as they're not above lvl 30, or they might not obey you.
Rinse, repeat, add some new content.
Maybe context sensitive events that aren't triggered until you get so far in another region.
