Strange, secretive, and desperately poor, North Korea tests the limits of social control.PYONGYANG—Here is the locked ward of the political asylum, the place where politics has actually become an official state religion, and power is worshipped, directly and literally, in the form of a colossal bronze idol to which the people come and bow with every sign of reverence. Nothing in the modern world compares with North Korea, though it gives us some clue about how life must have been under the pharaohs, in Imperial Japan before Hiroshima, or in the obliterated years—conveniently erased from memory by blushing fellow travelers—when...