The "nobody exists except US" attitude can show up in surprising places. One TV movie set after a Soviet invasion of the U.S. had a briefing for people being released from a "re-education" camp. There was a map on the wall - the standard "disembodied United States" map used by TV weather forecasts. If the Soviets were to invade the U.S., why wouldn't they also invade Canada and Mexico? Also, why would they make any distinction (other than which Soviet officer was in charge of various areas) between Soviet-occupied U.S., Soviet-occupied Canada, and Soviet-occupied Mexico?
The hypothetical invaders may well make their administrative territories based on natural boundaries anyway; so where the borders are arbitrary, they'd probably end up being changed.
There are only a few nations which would be likely to keep their current boundaries after a major war; and those are islands or island groupings, or places like Chile where there's not really any point in trying to cross the mountain range just to gain a few extra hectares of land.
Seshat's self-help guide:
1. Would you rather be right, or get the result you want?
2. If you're consistently getting results you don't want, change what you do.
3. Deal with the situation you have now, however it occurred.
4. Accept the consequences of your decisions.
My professional areas of expertise are computing and writing: I am not a doctor or a lawyer.
When your health, freedom, etc are at risk, always see a professional.