Don Boudreaux argues that trade promotes peace and that therefore protectionism as embraced by many anti-war types simply makes the world more dangerous:
By promoting prosperity, economic freedom gives ordinary people a large stake in peace.
This prosperity is threatened during wartime. War almost always gives government more control over resources and imposes the burdens of higher taxes, higher inflation, and other disruptions of the everyday commercial relationships that support
When commerce reaches across political borders, the peace-promoting effects of economic freedom intensify. Why? It’s bad for the bottom line to shoot your customers or your suppliers, so the more you trade with foreigners the less likely you are to seek, or even to tolerate, harm to these foreigners.
Don has a link to the empirical research at his essential blog, CafÃ© Hayek.
One might add that Dominique de Villepin and others have been suggesting trade barriers as a necessary element in combating global warming. I shan’t cheapen the debate by calling them warmongers, but we shouldn’t be blind to the likely consequences of such an approach.