A third recommendation for Nothing to Envy.
I've read several books on North Korea, and it's mind boggling to try and comprehend the amount of brain washing and enslavement of the North Korean people. Peter Hitchins described them as a land of "racist dwarfs" because they've been brainwashed into fearing the rest of the world and literally starved to the point of being stunted in height.
North Korea has always issued shrill, hysterical threats to the US and South Korea, but their recent rhetoric has gone even further and they're belligerently doing missile tests and working on nuclear weapons.
China has always sided with them. For decades, North Korea was propped up by the USSR and China. Then the Soviet Union collapsed, and they began to fall apart. China still sided with them but now it seems that China is more interested in trade with the West and has been less supportive of late.
South Korea is probably less afraid of war than with the prospect of 25 million impoverished North Koreans (who are still legally citizens of the South and entitled to aid and benefits) streaming in, ignorant, helpless, and ill prepared for life in a capitalist society.