North Korea got oil supply? No oil, no need bother yet.
Seriously though, I think simply attacking N.Korea would be a
terrible decision, namely because N.Korea has close ties with
countries such as Pakistan, which would complicate things further,
plus these countries are suspected to have nuclear
capabilities.
The only possible way I think would work would be an internal
revolt and reformation when Kim Jong II steps down and power
shifting happens, but I guess the people are too suppressed by
now.