You know, after Homefront came out, I struggled to think of a more implausible villain invading the US then North Korea and couldn't think of any. It turned out that the UN was the even more implausible villain I was looking for.
It doesn't work in the Left Behind books and it doesn't work here. The only way it works is it you set it in some kind of an Alternate Universe where the UN was granted massive amounts of support by the major nations during the cold war(or maybe afterwards) so it actually poses a legitimate threat as opposed to "We will be very angry and send you a letter telling you just how angry we are if you don't stop your genocidal tactics" they are in real life(wherein, most countries just respond "Send all the nasty letters you want. We have a paper shredder")