Principled in that they didn't fall into either the Soviet or PRC camp, they called it like they saw it and their foreign relations suffered for it. The idea of self-reliance was put in place because trading partners were either gone or undependable.
Principled in the sense that just a decade later they came up with the ideology of juche? Complete self-reliance in order to stop accumulating debt is what it essentially was. Super protectionism that completely failed.
True, China isn't imposing sanctions, but to say the two countries have been good friends is an oversimplified view IMO. I also think the DPRK doesn't want to be tied too close to China economically lest they lose all economic independence...once a country gets into an economic pattern it's very hard to break out of it.
China's imposing sanctions? You have the fastest growing economy in the world right next door who is more than willing to trade with you and you blame US sanctions for all the problems? It has everything to do with keeping outside information from coming into the country. People will start to ask why China is doing better than them and the facade of the Great Leader would begin to collapse.
As far as trying to keep information away from DPRK citizens, the head of the World Health Organization's statements that the DPRK's medical system is the envy of the developing world changes the equation: perhaps western countries don't want Cambodians seeing DPRK hospitals since they will start to ask why their country has so few quality hospitals and the myth of benevolent capitalism would fall apart.
OK neat, I'll check out some of his work if I can find it.
Russian professor who teaches in South Korea, studied Korean history in North Korea. Overall his insights on the North are top notch.