The worst thing we could do is put troops on the ground in N. Korea, we would have another Vietnam on our hands in my opinion. Carpet bomb the country, target nuclear facilities and if necessary sent the South Korean army in.
Probably an easier solution would be to kill Kim and all his generals in one strike. The citizenry will take care of the local apparachniks after that and then China and South Korea could figure out what to do next.
We are not going to invade North Korea. That would be stupid. The whole country is a somewhat rusty and underfed but armed camp.
But there is a risk of North Korea attacking Southward.
We already have troops on the ground in Korea since the treaty.
I would prefer creating the Island of South Korea, sending all of North Korea straight to Hades
Let Japan, South Korea and the rest of the allies there do the ground work. We can supply them, not fight for them.