Oh, be still my heart!
UN troops in America - a chance to eliminate both Foreign and Domestic enemies at the same time! Excellent. The stuff every redblooded American patriot has been dreaming of since Jane Fonda was still an attractive little whore conspiring with the enemy!
I'm reminded by the quote from Gen. Lewis B. "Chesty" Puller:
"All right, they're on our left, they're on our right, they're in front of us, they're behind us...they can't get away this time"
The US divided into 7 districts? That makes for a great deal of "border" to enforce. Although it has some advantages, it also has drawbacks.
What would be the potential for foreign intervention by UN forces or others?
Not much I would think. At least in the sense of making a strategic military difference. It doesn't seem likely that the French or Dutch or Germans would lend many (if any) troops to a UN "peacekeeping" force deployed in the US. However, I can see Obama getting a small number of forces that could be technically seen as UN involvement. Just enough to make the claim that it is a "multinational force" helping restore order. Complete BS, of course.
OTOH, if we envision an international economic crisis / collapse that enabled Obama to justify martial law or such, it seems unlikely that anyone in the EU would be in the condition to loan out troops. The $hit will be hitting the fan everywhere in the west.