Why does North Korea want nuclear weapons? Apparently, Americans find this completely mysterious. Indeed, rather than even attempt to consider the question, they simply define it out of existence by asserting that the leadership of North Korea is irrational and evil. End of story.
However, the world is not peopled by characters from morality tales. People are far more complex than such stereotypes. That includes the people and leaders of North Korea. Kim Jong-un isn't a pantomime character.
North Korea wants nuclear weapons because it feels threatened. And it feels threatened for good reason: it feels threatened because it is threatened. The leaders of North Korea know that the US wants regime change. The leaders of the US have hardly made a secret of this fact. It has been the US goal for decades. The leaders of North Korea also know that the US has a track record of going around the world overthrowing sovereign goverments. Since the Second World War, the US has kiled over twenty million people. It has overthrown at least thirty-six governments. It has interfered in the at least eighty-two foreign elections. It has attempted to assassinate more than fifty foreign leaders. And North Korea's leaders are well aware of this history (apparently it is only some Americans who are not).
The leaders of North Korea are also well aware that the US has its military amassed on its borders. It has tens of thousands of troops on North Korea's southern border. It has warships and planes off its coasts. Every year the US engages in military exercises to practise the invasion of North Korea. If the situation were reversed no American would dream of claiming that North Korea was not the aggressor; yet with all the appearance of sincerity they claim the US is not the aggressor.
The US has imposed sanctions on the people of North Korea, imposing severe economic hardship on the people. (Collective punishment is incidentally a war crime and a crime against humanity, although everyone pretends not to know.) The US political-media elite, for the purposes of domestic propaganda to a sentimental audience, then hypocritically exploits the economic hardship as proof of the evil nature of the North Korean leadership, as a justification for sanctions and the threat of war. A vicious circle that is designed to destory North Korea's economy and thus cause the collapse of the society.
Seeing all this, the desire of North Korea for substantial military defence, including nuclear weapons, is entirely rational. Without such military forces, North Korea would have been invaded long ago, as happened to so many other countries that refused to be vassal states of the American empire.
The latest move in this strategy to destroy North Korea was the United Nations sanctions. This was, however, only a partial success for the US. It steps up the sanctions and having the votes of Russia and China provides the fig leaf of "the will of the international community". But the sanctions will have little actual impact. The supposed cutting of North Korea's exports by a third is merely creative statistics. The cut is supposed to be primarily achieved by China's cutting of coal imports, which was put in place at the beginning of the year. In other words, the new sanctions merely codify and legitimate the previously existing sanctions. Moreover, the unstated quid pro quo that the US gave Russia and China was an agreement to seek negotiations, something US ambassador Nikki Haley had ruled out only a week earlier. More tellingly, North Korea is not going to give up its defence programmes, as the US is well aware.
Since Donald Trump became president, he has ramped up the tension between North Korea and the US, bringing the world dangerously close to a war that would inevitably cost millions of lives. At the moment, Russian and principally Chinese diplomacy seems to have halted that rush to aggression. How long that impasse can hold is unknowable, but it is anything but stable. And that is why North Korea will not give up on its defence programmes, especially its nuclear weapons and its missiles, as they are its only guarantee against naked US aggression.