At this point it has nothing to do with "preventing democracy" (if it ever did). All countries want to prevent the massive refugee crisis that would exist if North Korea suddenly falls. I think something should be done but I don't think anyone currently has a good answer to that situation.
You are acting as though it's questionable whether Stalin and Mao got involved in the Korean War to prevent the spread of democracy. Check out the book The Great Leader and the Fighter Pilot. It covers the history of the Korean War and Stalin and Mao's actions. Also, a really great story about the famous fighter pilot No Kum-sok.
