Best case scenario (imo) is boots on ground cooperative with South Korean troops, bringing fucking culture. There's a reason missionaries are able to set up such successful excursions into 3rd world countries. They bring food, technology, education. The new PM of South Korea seems very benevolent, and I bet would let North Korea remain their own state if they so chose to.

So testing missile distance, explosion strength, and firing over Japan is to do what again?

Is to show the world that NK will defend itself no matter what. 

They are actually proceeding in a fairly logical manner. They know full well what happens to "regimes" like Saddam Hussein who didn't have nuclear weapons. Those are the guys that end up dead. 

Kim has no intention of being one of them. Nuclear weapons assure NK that the regime will live on, and even more than that, they can use their belligerience as a bargaining chip now. "OK, we'll stop firing missles over Japan, but you have to stop treating us like a rogue state and we want economic kick backs".

It's actually fairly well played on their part. They've taken a pretty shitty poker hand and maneuvered themselves into a strong position by betting everything on nukes.  

No. NK likes to bluff alot. It's gotten to the point, you can't take any of the bluffs seriously. It's like the short guy running his mouth to make up for his size. So preemptively attacking NK on the basis that they are being serious with their threats wouldn't hold any water these days regardless of what party chooses to it. I'm all for protecting ourselves but they'll have to strike first to give the US/Japan an ironclad justification for war. Plus, China and Russia will more likely side with the US/Japan in that scenario. Preemptively attacking NK might start a war with China and Russia because the justification would be really flimsy.

Yeah but in this case, the short guy has a loaded gun. 

To defend itself from a country that it has habitually antagonized and demonized, right?

In fairness to North Korea, it is the US that went to war in their country. It is the US that surrounds their border with military bases and runs military drills simulating the destruction of their regime. 

It's not so easy to bully a country when they have nuclear weapons, most likely the US is going to have to swallow their pride here and conceed certain things to North Korea. 

That's what a lot of people thought about the USSR vs. USA, and that didn't end in nuclear annihilation.  Doing a pre-emptive strike without China's approval could have far worse consequences than holding back. 

I don't feel concessions should be made to any country that tries to pick fights with a super power just so it can continue being a massive cult.

WW3 will be machines destroying humans. Relax guys.