A NYT article by Anthony Banbury, an American senior UN official who has resigned after thirty years service. Here is key reason:
But in terms of its overall mission, thanks to colossal mismanagement, the United Nations is failing.
His slim Wiki bio:https://en.wikipedia.org/wiki/Anthony_Banbury

Some harsh comments on several UN peacekeeping missions: Haiti, Mali and CAR too.
Link:http://www.nytimes.com/2016/03/20/op...ling.html?_r=0