Just look at Nazi Germany and Soviet Russia, both having extensive trade relations with one another, yet war broke out. The theory has also been restated as the Golden Arches theory of war, the idea that having a McDonalds represents an economic development level were war becomes increasingly unpalatable between the two nations, which has been dis proven multiple times.
A nation's foreign policy is shaped by externalities around it. Switzerland and Canada aren't neutral nations militarily out of the kindness of their national character; no, they do so because they can achieve their ends via other means and because it would be difficult for them to use military means to achieve their ends. France, for all its bluster about American warmongering in Iraq and Kosovo, had no problem joining a conflict in Libya when it thought that she had something to gain from it. China and Russia's calls for caution in Syria, and opposition to the invasion of Iraq, have nothing to do with respecting the sovereignty of nation states, and everything to do with their own interests.
Either way I have rambled long enough when Mr. Kaplan and Mr. Friedman do a much better job explaining the theory of geopolitical forecasting and their own ideas on it.