Most other countries will try to side with the left, even our so called 'allies'. It is not going to be as one sided as you might think. The usual suspects will take advantage like China, Iran, N. Korea, Russian, Cuba etc.
Best scenario: We keep our guns and they don't do anything about it. If the left can come up with Sanctuary States, so can we.
My opinion is all have already taken sides, with it simply being matter of good vs. evil. Forget about national boundaries, the evil ones are always drawn to each other, and yes you are right, we are pretty much alone. Most will side with the left, but good will triumph with Jesus returning and casting the evil ones into hell.
Your sanctuary state scenario kicks the can down the road, we wont get to that point.