I was going to list, individually, all of the many acknowledged failures of the U.N. from:
Bosnia here and here
and including the whole Oil for Food Scandal that placed 10 Billion dollars in Saddam's pockets,
but it would take far too long. So, for those of you who think that the U.N. has been anything but useless, the National Center for Policy Analysis has a list of the many failures in addition to the few successes. Note the major difference between the two.
Many human tragedies could have been averted had the U.N. acted accordingly. When you don't act soon enough, or cut and run before a task is finished, or tie the hands of the Peacekeeping Force by not allowing them to engage unless fired upon, then you have trouble.