How effective is the UN in dealing with security challenges in the 21st century?

How effective is the UN in dealing with security challenges in the 21st century?

The essay is at Masters level and need to be no more that 4000 words (including footnotes but not bibliography). It need to argue that the UN is struggling to keep up with the pace of change in modern security threats and quote the big names of international relations such as Barry Buzan etc. It will need to use the Chicago referencing system. If the paper is good, i have plenty more that need doing.