Your delusional if you think China is stopping America from North Korea. A lack of resources is stopping a war with North Korea. Saudi has resources, they sell them to us and we look the other way. If we don't they go to Russia and China. Why not take nice cheap resources.
Do you realize how powerful the US military is? Noone is even close. It's as if you put a cat in a cage to fight a German Shephard. That goes for every country. The US spends as much on military as the following 9 military powers combined. That's Canada, Indonesia, Germany, Poland, Thailand, Australia, Isreal, Taiwan, Egypt, Pakistan, Turkey, United Kingdom, Italy, South Korea, France, India, Japan, Russia.
We can smash North Korea before they knew it, eliminating any hint of military force they have as if we were swatting a fly. It would be so easy it's unreal. The largest risk is any sort of failed execution which would lead to mortars heading towards Seoul.
North Korea only has labor but for now China and India have plenty of cheap labor and it's far more stable and skilled than N Korea. Not to mention the investment it would take to utilize that labor as there is a complete lack of infrastructure and any resemblance of formal education. Your talking a huge investment for very little return in a time that the resource of human labor already exists and will exist for the foreseeable future. That is why we don't bother with North Korea. No country on the planet wants the burden of North Korean people. Nothing economically to be gained, America and everyone else doesn't give a shit about human rights.
For China they do utilize this labor as essentially free labor. Just Google "Chinese using labor from North korea". All about the resources. In my opinion is the one of two primary reasons they are allies. China make very calculated moves, in the event of any actual war I suspect there is little China can or would do that wouldn't cause their economy to collapse. The second issue is they don't want South Korea or a US presence so close, furthering the 'alliance'.
Sorry on mobile please forgive any grammar or typing mistakes.