You don't know alot about geo-politics, do you? No war is going to break out. If the North ever actually started a war with Japan (and the West) they'd lose in about 1 day. The North is hopelessly outmatched by the West (or even just Japan). The reason a strike has not happened yet is a) Seoul would be destroyed first, because North Korea has hundreds of thousands of artillery pieces lined up aimined at the South Korean capital... the the Americans, they kind of like Seoul, b) NK's nuclear weapons (although few in number, and useless in battle situations because they cannot be fired at all, let alone accurately across countries) complicate the situation, and c) the consequences of the country collapsing (as it would under a unilateral strike) would be catastrophic. Millions of refugees would flee to China and other countries. The North couldn't even hope to man a long term counter insurgency, since unlike in Iraq, the people would be relatively supportive of regime change (not that the US would send in ground forces) because it is the most F#@$'d up country on Earth. Things there are so bad, they literally could not be worse. Nobody has enough food, nobody owns anything, you are killed for owning a mobile phone, everyone is forced to god worship their leader (and his dead relatives), nobody knows who to trust, etc. It's the closest anyone has come to a 1984 police state.
I doubt North Korea could even hit Japan with a single rocket before the US destroyed their artillery ranges and defences (given they don't have accurate ICM's or anything with that kind of distance). Seoull however is too close, it's right next to the border, and normal artillery can hit it. You need to stop watching James Bond films. The North Koreans are helpless against the West.