MERCOSUR and the EU predictably come to mind. The US, I think, treats Canada and Mexico very differently from other nations (being a neighbor); North America is fairly unified. The US doesn't hold up its non-interventionist/isolationist end of the Monroe Doctrine, but the loose North/South American protectorate set out by that diplomatic philosophy certainly holds true today. MERCOSUR is a good example of nations asserting their sovereignty with a trade bloc rather than via national posturing, weakening this protectorate.

I can't provide links (books are of greater help when synthesizing theories for me) to prove this, but I do recommend reading up on the aforementioned trading blocs, as well as this excellent book: http://www.amazon.com/End-Nation-State-Regional-Economies/dp...