National boundaries are not static. The Soviet Union, Czechoslovakia, Yugoslavia, Serbia, Sudan, and Ethiopia have all split up in my lifetime, while Germany merged from East Germany and West Germany as did the two Yemens. E. Timor gained independence from Indonesia. Hong Kong and Macau reverted to Chinese control. Colonial arrangements in Panama, Palau and if I recall correctly the Marshall Islands, ended. Kuwait was briefly erased by Iraq and then was restored. Western Sahara has effectively been wiped out by Morocco, UN efforts to the contrary notwithstanding.
If Catalonia (in Eastern Spain) were to gain independence (an increasingly plausible idea), or even federation status, Basque Spain (in Northwest Spain) would surely follow. Northern Ireland could seek independence from the United Kingdom, and Scotland could change its mind and leave after rejecting this option in a recent referendum the first time around. And here are some other possibilities (renumbered by me from the source), with my own new additions as well:
1. Belgium could split up into French and Flemish kingdoms.
2. Somolia's de facto multistate division could be recognized.
3. Korea could be reunited if North Korea were to collapse.
4. Mali could break up on North-South lines reflecting Islamic control.
5. Nigeria could break up on North-South lines reflecting Islamic control.
6. Congo could split up into multiple states.
7. An Alawite State could be carved out of Syria.
8. Iraq could break into multiple states including possibly an independent Kurdistan in the Northeast and a Shiite Sumer state in the Southeast.
9. "Sunnistan" could be created in what is now ISIS territory.
10. The Arab states of the Arabian Pennisula could enter into a union or federation.
11. Azerbaijan could expand its territorial area of Azeri control into Iran or other neighboring countries.
12. Afghanistan could splinter into ethnic regional sub-states.
13. China could obtain some or all of Siberia from Russia. Likewise, it could acquire Mongolia.
14. Normandy, Brittany and/or Corsica could seek to leave France.
15.The Balearic Islands of Spain might join Catalonia.
16. Tibet could gain independence somehow.
17. One or more of the Caucasus states could gain independence from Russia.
18. Russia could absorb Belarus much as it recently absorbed Crimea from Ukraine.
19. Ukraine could split on East-West lines.
20. Yemen could split into a Northern Yemen and Southern Yemen again.
21. Quebec could gain independence from Canada.
22. Puerto Rico could gain independence from the United States.
23. Taiwan could rejoin China.
24. Thailand could break up on Muslim-non-Muslim lines.
25. Colombia could split into a narco-state in the interior which was the de facto reality for some time and a rump Columbia.