Not completely accurate, those Japanese mothers jumped off the Okinawa cliffs because they were made to believe that if they fell into the hands of the Americans, they'd be raped, tortured and killed alongside their children. Not because they were defeated. That death before defeat mentality did exist in Japan, but not to the extend we are made to believe. Many Japanese were Buddhist for example.Nobody is taking the Korean mentality into account here. Similar in ways to the Allies fighting the Japanese in WWII, in that the Koreans would be the type of brainwashed enemy who WILL die to protect their country, and would rather die than lose.
Japanese mothers were known to jump off cliffs with their children, rather than face defeat, hence the reason the A-bombs were dropped. They couldn't be beaten by head to head fighting, they simply had to be completely crippled tactically.
As far as the US telling people not to have them, that's a bit of a joke. They have more than all other countries combined and are the only country to have ever used them. However, the UN said NK can't have them, so in that sense the US is allowed to wave its fists. Also, Obama has expressed a strong desire for nuclear disarming.
As far as NK doing the testing goes, it's just business. Most likely there is another famine, the country is now totally broke or something along those lines. Look at the last 50 years: Every time NK needs something, they do something that upsets the world and makes them look scary. The world then gives them money and aid and all is well again for a few years. Until Kim runs out of Oreos again and he does another test, demanding more cookies. That is all.
North Korea would never start a war. Not even against the south. They are the brokest country in the region and despite their parading and goose stepping, their military strength is laughable. And Kim knows that. If the Chinese hadn't intervened, NK wouldn't even exist anymore and back then the people were still full of revolutionary zeal. These days they know the grass is greener on the other side, they are just not allowed to say so in public. There is a very large underground movement in NK that the government doesn't want the world to know about.