In this article, it states that North Korea wants to re-evaluate their building of nuclear weapons, but the United States fear because North Korea could actually build such weapons that can either reach Los Angeles or Washigton. It also states the history of the development of Japan's nuclear weapons developement, which it began in the 1960's. It talks about the Nuclear Nonproliferation Treaty and how it's used.
In this link would give you the full article with more detailed and how the nations itself would be facing the fear of the development of nucelar weapons.
North Korea Rouses Neighbors to Reconsider Nuclear Weapons