Neither North nor South Korea had endogenous political development, and indeed North Korea is the last holdout of Soviet-style centralised power while South Korea has been heavily influenced by the US in is development. You might say it's been a "brutal success"; it has the economic development and seemingly everyone gets fed, but lacks political freedom. The US had a seemingly positive influence that was not available to North Korea; this is not a case of the US's "fault", not a result of active sabotage (unlike several countries in South America).

http://www.bbc.co.uk/news/world-asia-19697171

"Behind the stellar growth were sacrifices by workers who suffered under a repressive labour environment," she said.

"Behind the efforts for national security to protect (ourselves) from North Korea were human rights abuses committed by state power."

It seems to me the evidence supports the conclusion that communism is a miserable failure and the idiotic policy of trade sanctions and other forms of antagonism makes an already bad situation considerably worse.