In the 21st century Countries such as the USA, UK, and Russia should be striving to reduce the nuclear weapons to zero. The US spends much money on defense and could easily intercept any kind of threat without the need of nuclear threats. Any threat the North or South Koreans may be to US interests could be easily countered by the US and/or China.
Countries that have access to nuclear weapons are always going to present a danger. Not only are nuclear weapons a danger in the wrong hands in a world where any politician could quickly develop a set of said wrong hands with enough power under his belt, but they also present a security risk when they can easily be stolen or compromised.