NK-no, China-I seriously doubt it, we may get into it with them someday but I doubt they will ever come for our homeland, maybe Hawaii or Alaska, but not the contiguous 48.

North Korea and China are both heavily dependent on food imports because of their massive populations. All it would take is a trade embargo on food imports, and we could starve tens of millions of people. I seriously doubt either of them would take that risk.

Good luck getting by the largest and most powerful Airforce and Navy in the world.

No, we might be in debt with China, but China is also dependent on our investors and our factories setting up there that gave them so much economical power. North Korea's army is too small to invade any superpower countries. Even if they conventionally invaded US, they'll not be able to take over, since we knew every square miles of our own terrain, most of our army settle here, our ammunition and supplies are much easier to access in our own country than in Afghanistan, plus we got many of our citizen with assault rifles and hunting rifles. Also, due to nature of the continent, any attempts to cross Pacific in the vicinity of the US will have to endures storms of Tomahawk missiles, fighters, submarines, and frigates.

Of course, we may have millions of Asians here, but they're loyal to their new home, they'll fought along with US even if they're invaded from country that their ancestors are from. Only extraterrestrial being could successfully invade US.....

Not now in 2015 because it would be a costly blunder. Maybe sometime in the future, an invasion could happen.