In addition to the points raised by Dayuhan about the scope of the essay and by davidbfpo in general I wanted to throw in some personal views:

1) I'm in general quite sceptic about the use of a too sharp schema of "new" and "old" wars. In fact I do believe that those conflicts described as "new" types have even older roots and have ever been part of the history of humankind. Only in some parts of the world they have been overshadowed in relative recent times by the those described here as "old" wars.

2) The UN has for obvious political and to a lesser degree legal reasons an easier time to efficiently act when there is a relative strong consensus about the problem and the mandatem, when there are distinct persons and institutions with which an effective interaction is possible. This hardly goes only for the UN or other international organisations but is in general even true in the private sector.

3) In short having the UN is, as written before, on balance then not having it. It even can be far better under some circumstances, especially when it has a narrow mission. As the US and it's Western allies have experienced even a vast amount of ressources and direct control over efficient national means can result in little progress when the local institutions are largely ineffective and the situations chaotic.

P.S: I do not understand the distinction between "Liberals" and "Realists". Thanks.