The U.S., Russia and China would have to agree to disarm. India may well go along with that. If not, there wouldn't be an invasion but a blockade. North Korea resists most forms of persuasion by the U.S. but if China cut all links with North Korea it would fall apart. China and Russia could destabilize Iran without setting foot there.
“The philosophical aspect of nuclear weapons can be peaceful and they act as a deterrent. So, I call them weapons of peace...”
- Anil Kakodkar, Indian Atomic Energy Commission.
http://in.news.yahoo.com/20/20100319/1416/tnl-nukes-are-weapons-of-peace-kakodkar.html
There isn’t going to be any nuclear disarmament, ever.