North Korea has officially declared that it has nuclear weapons. North Korea, perhaps taking a lesson from Iraq, says it needs the weapons as protection against an increasingly hostile United States. It's hard to tell whether the current statements are nothing more than NK's trying to bolster its bargaining position or as a warning against possible U.S. belligerence. If NK has gone nuclear, it seems like Japan would have little reason not to follow suit.
The Barking Dingo has a much more detailed post on this.