First a few caveats before I paint the broad strokes for the perspectives and motivations for the major players as they relate to North Korean strategy.
I haven’t studied international and public affairs. I believe, nonetheless, that the broad strokes below describe the important aspects of the strategic situation. Perhaps I’m speaking out of ignorance, but I believe history backs me up: how else can you explain a regime maintaining power with no resources defying major global powers to build nuclear weapons, counterfeit the dominant powers’ currency, deal arms and drugs, and oversee the preventable deaths of ten percent of its population?

The North Korean Government

The North Korean government controls the lives and economy of North Koreans more than most other countries. The higher up the officials within the power structure, the materially better off they are. People at high enough levels even in the midst of great famine lived comfortably.
The North Korean military is large and powerful within the country, though not likely powerful outside, except that they have nuclear weapons and conventional missiles that could reach Seoul and probably Japan within minutes.
The North Korean government controls the flow of information and people across its borders more tightly than probably any other country. The country has virtually no access to the internet or any press independent of the North Korean government.
Wikipedia, while citing that the North Korean government claims it has no human rights issues, cites many sources reporting that the North Korean government punishes and tortures political prisoners and those who speak out against the government.

The North Korean People

The perspective of the North Korean people is, I think, the hardest for people to understand. Putting yourself in their shoes requires forgetting most of what you know about the world. The North Korean people are ordinary people like you and me, just with little independent information about the outside world or their government.
As best I can tell, people there realize life is difficult, but believe that no place else is better, that they have nothing to envy.
Also, they face draconian punishments for acting against the government — their relatives and loved ones can be punished. The can be jailed and tortured for minor offenses, or possibly arbitrarily.
The result is effectively widespread compliance with the North Korean government, which effectively supports it.

The South Korean government

North Korea effectively holds South Korea hostage with its missiles that could kill countless South Koreans in Seoul in minutes and wreck its economy. Despite the size of North Korea’s military, the United States could defeat it militarily. But in winning that war, it could lose the battle of Seoul.
Though they speak the same language and have many families separated for only a few decades, the relevant issues regarding North Korean strategy for the Koreas are the missiles pointed at Seoul, the U.S. presence in South Korea, and the difference in sizes of their economies.
North Korea invaded once before and might again were it not for the U.S. presence. North Korea’s occasional belligerent action against South Korea reinforces that they just might attack. Those belligerent acts make them seem crazy to us, but they strengthen their position. The more we think they might act crazy if we paint them into a corner or attack, the more credible their threat. Since such actions also affect the South Korean economy, it shows the strength of North Korea.
No matter how much stronger the U.S. military, within minutes of invading, tens of thousands in South Korea could die. No one could accept those losses. Those missiles hold South Korea hostage.
South Koreans also know how much bigger their economy is and how negatively East Germany’s economy affected West Germany’s after their reunification. South Korea has little incentive to unify with North Korea.

The Chinese government

China shares North Korea’s largest border. China has historically supported North Korea as another communist country. North Korea also puts a buffer between China and the U.S. military in South Korea.
I think China’s perspective is that they don’t mind supporting an oddly behaving country and its leaders in exchange for that buffer from the U.S. That support probably doesn’t cost them much materially nor too-badly affect their standing with other nations.

The Russian government

Russia historically supported North Korea as another communist government. That support fell drastically with the fall of the Soviet Union. Russia’s border with North Korea is small.
The Russian government could take a significant role in North Korea’s strategy, but I don’t think it has motivation to play a role comparable to the other players. As long as it does little, North Korea looks benignly at it.

The Japanese government

North Korea claims to resent Japan for invading it, Kim Il Sung grounded much of his identity in liberating his country from Japan, and their propaganda presents Japanese as imperialist aggressors, like Americans, but less so.
North Korean missiles can reach Japan so Japan is motivated not to provoke North Korea, similarly to South Korea. It is also a hostage, though at less of a risk.

The United States government

North Korea propaganda describes the United States as an imperialist aggressor that began the Korean war, keeps the Koreas from unifying by continuing to occupy South Korea, and hurts North Korea through blockades and sanctions.
I think the bigger issue, from the North Korean government perspective, is that they believe they could reunite with or maybe overpower South Korea if not for the United States. They see the U.S. as stymieing them from improving their country.
The United States government would probably see North Korea as not worth much attention but for two major issues. First, North Korea developed nuclear weapons and would probably target the U.S. first if its government felt painted into a corner. Second, North Korea supplies other countries with weapons and drugs.

The North Korean government again

The North Korean government recognizes its nuclear weapons force the world’s largest military to respect their power. This motivates them to maintain that program.
The missiles North Korea points at Seoul, along with the nuclear weapons it could use in the United States, protect the country from all military action or invasion. They would lose any war, but not before inflicting unacceptable losses on anyone else.

Summary

All national leaders gain from maintaining the status quo.

• Decision-makers in the North Korean government live well and would risk their lives to allow North Korean people from learning what the rest of the world says about North Korea.
• The North Korean people, as far as they know, live fine, perhaps better than others outside North Korea.
• The South Korean and Japanese governments don’t want actions that could provoke a trigger-happy neighbor to retaliate militarily.
• The Chinese government wants to maintain a buffer between them and the Unites States presence in South Korea.
• The Russian government is taking a relatively minor role relative to the others.
• The United States government doesn’t want to take actions that could hurt its allies in South Korea and Japan.

Next: North Korea’s sustainable competitive advantage
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EDIT: I included much of this post and this series on strategy (edited and polished) in my ebook, Understanding North Korea: Demystifying the World’s Most Misunderstood Country. I wrote the book to help increase understanding, communication, and freedom.