The US has long had the principle to have the best trained, best equipped soldiers, and to let the other guy throw human waves against their enemies.
There would be no conflict because the 37 miles to Seoul or whatever it is would be fast a killing zone for those millions of soldiers.
In any case, this isn't about an actual military invasion. It's about threatening the West to get some economic concessions (and probably, secretly, some 9-10 digit sums in some bank accounts in Zurich) to get them to stand down on their aggressive stance and nuclear research. Then they just wait awhile until the piggy bank gets empty, and repeat it all over again.
It's like a bully in school who gets bought off with lunch money, only to come back again the next day. Their behavior never changes because the principal of the school keeps saying, "If you do it again, I shall give you a stern talking-to again!"