The playing field for North Korean strategy, which reduces the number of relevant players, simplifies North Korea’s strategic situation more than almost anything else. Few other nations see such a combination of global importance and simplicity.
The map below, from Wikipedia, shows nearly everything you need to know about the playing field.

North Korea shares borders with three countries: China, South Korea, and Russia. Farther to the east lies Japan. No other countries are close.
For a few reasons, mainly that North Korea developed nuclear weapons and its involvement in the Korean War, the United States is involved.
Within North Korea I distinguish between the government and the people.
Each of these players contains multitudes of sub-players with divergent interests. Nonetheless, I think treating these seven groups as the relevant ones and each one as homogenous gets the main structure.
The main players are

• The North Korean government. Kim Jung Il is the head. In many countries the division between the military and civilian power is significant. I treat the government as one monolithic entity.
• The North Korean people. They obviously have diverse interests, but one relevant common behavior: they don’t rebel against their government.
• The South Korean government.
• The Chinese government.
• The Russian government.
• The Japanese government.
• The United States government.

The United Nations and the people of the other countries play minor roles, but smaller than these players.
Back to the playing field, China has a long border with North Korea and Russia has a small one, both allowing people and goods to pass. South Korea has a long, heavily fortified border that allows almost no people or goods to pass. Japan is an ocean away. The United States is nowhere near, but has a strong military presence in South Korea.
Next: Relevant players and their motives
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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.