The basic idea is that, in some regions, vast empires were only possible if the state had control over access to water. Control of the populace was ensured because everyone would soon die if the crops were denied the life giving resource.
A drought was, oddly enough, a way for the reigning despot to strengthen his grip. Scarce water would be diverted to cities and regions that shown the most enthusiasm in their support of the ruler, while more troublesome populations would have to face a terrible death from starvation. The favored were even wilder in their support, while anyone who was less than loyal wasn’t around any longer to cause trouble.
Strategypage.com reports that North Korea has been doing the same thing, except that this time it is food that is scarce instead of water. The armed forces spend a fair amount of their time farming and raising food, which means that the guys with all the guns are less likely to rebel. Civilian farms in areas known for showing signs of unrest are denied desperately needed supplies, which results in mass starvation.
Policy towards North Korea seems to be based on the hope that it will eventually implode on its own. The strategy is that forces inside the country will destroy the odious Communist government if we wait long enough. It is hoped that the people will rise up just as soon as enough of them realize that they have been lied to by their leaders, or the remaining leaders will start a civil war after Kim Jong Il dies.
I first came across the theory of hydraulic empires when I was reading the Larry Niven novel A World Out of Time way back in 1976. The protagonist explains the concept, and then mentions that this type of empire exerted such control over the population that they could never be toppled from within. The society might become so rotten that a single barbarian raid could start a chain reaction which led to the destruction of the entire empire, but it always took that push from outside to get the snowball rolling downhill.
Things are a bit more complicated when it comes to North Korea, mainly because both China and South Korea have an interest in seeing the country lurch along without coming apart. But, even if Pyonyang didn’t have their support, I would be willing to bet that the government still wouldn’t fall on its own.