north korea i can imagine would start a war just out of their stupidity.
china supports them because they are a communist country that borders china, and will not support anything UN.
china dont have to like how n.korea runs things for themselves to still support them and use them strategically.
countries all trading with each other and generally not being at war does not mean we are friends.
the cold war technically isnt over. and there are more super powers having an arms race then ever before.
sure we play nice most of the time, we need each other for ALL of our economies. but we arent dependent on that as peace. we still all hate each other.