It's 2015 and the US and South Korea, tired of Kim Jong Un's human rights abuses, decides to launch a preemptive invasion of the DPRK under the shield of NATO.
top kek. not in the world would it happen. needs more background info, otherwise this is really unrealistic
The goal is to topple Un and establish democracy
under whom? the Chinese? the South Koreans? the US? the UN? a democratic DPRK?
it's preemptive, so the following could be expected from the ROK/US forces:
1. capture of nuclear arsenals
2. decimation of NK's large and decrepit artillery via air strikes
3. humanitarian aid to lure north koreans out from cities, then carpet-bombing
4. conventional infantry attack across the dmz(with use of anti-mine devices, I assume)
and so on and so forth.
It may be successful in that ROK/US wouldn't have a hard time defeating North Korea, but it may not be successful in that it will trigger a Chinese response, one that can undo ROK/US's military objectives.
my bet is that he wouldn't, even when NK is basically fully conquered. He doesn't seem that nihilistic.
Will Koreans be hostile to the invaders?
depends on how the war goes.
What if Japanese defense forces are used?
it'll open a can of worms, and I think the ROK/US ground troops would be enough to successfully conduct operations on their own. They can be useful in post-war pacification, however, and such a policy can help in increasing Japanese support in NK. Should be done delicately though.