Why is the leader of N.Korea so ruthless towards his people? Everybody would be better off if?

he learned to be compionate towards people rather than himself and only the elite who support him. I know that they are still bitter over the results of the Korean War, but unfortunately war at the time seemed like the only way to dissuade the N.Koreans from taking over S. Korea and possibly the world. Can't we all learn to be happy with what we have without having to impose hatred upon others. I know I'm going to get answers like "because there are people in this world who don't give a damm about others except for themselves and that they crave power in addition". Can't we all let people live in a democracy where everybody has an opportunity to be happy. It's so sad that threre are people who are like Hitler,Jong, etc who become rulers and end up hurting people. I know this sounds a bit naive, but, I think maybe we got to try to prevent people who are crazy -with a need for power over people, from getting elected. Can't we try to reason with people and be nice without having to force war or anger or provocation.