There are 2 types of player nations in Rival Regions: original (shown in green colour) and a displayed nation.
Original nation provides bonuses in wars only.
Displayed nation serves only for a roleplay and can be changed at any time.
From the start, your original nation was detected based on your IP address. That system can sometimes make mistakes, or you can simply live in another country.
You can change your original nation one time at the beginning of the month. When you change your original nation you can see the next available date on the same page.