PRNK should join USA against the real enemy, China

Well lets not forget that even China has had enough and voted in the Security Council against North Korea. i have said it before last year and I will say it again. China will quite happily let North Korea go to the wall if it steps out of line and plays with its nuclear firecrackers once too often. Let us not forget China has investments abroad and will not want North Korea messing around with that. I suspect China will allow the West to teach North Korea some manners in return for turning a blind eye to Tiwain for example. China knows that the USA or the UN wont be stupid enough to invade China and are more interested in just sorting out North Korea.

How will an underground nuclear test lead to nuclear war?

As for the hydrogen bomb theory, they have to build a working nuclear weapon first, and use that as a stepping stone to get to the hydrogen bomb.