Stop using American words.
Fragment of a discussion from Comments:Greek debt deal reached
It has long been standard to use UK English in European articles. Assuming "an OAS" is an Organization of American States member then I would certainly support use of American English there. You're pushing it a bit by the time you reach the extreme south, mind. Europe is much smaller. That said, I wouldn't be opposed to anyone who chose to make US English the choice for the whole lot, except for any where there is some reason why an alternative form that might be better (I don't pretend to know the ideal for every country). Without doubt, any North American country should be getting the US English treatment.