Rage as a psychological variable, because your research is in social and political psychology. You can measure it by psychological scale, where e.g. half of its items will be positively (e.g. ''I have a positive attitude towards America'';  ''I agree with American external politics and actions''...) and the other half negatively defined (Generally  speaking, I am against America's political actions.'', When somebody mentions USA, I become angry and feel some kind of rage toward it.''). For every item, you could provide a scale such as Likert's 5-point scale, where 1 means ''absolutely disagree with this item'', 2 - disagree, 3 - indecisive, 4 - agree, 5 - completely agree...

This isn't rage, but Larry James and his students developed a measure called the Conditional Reasoning Test (CRT) that indirectly measures aggression. If you found differences between samples in traumatized and non-traumatized communities, I think that might support the type of hypothesis you are suggesting.

http://orm.sagepub.com/content/8/1/69.abstract

Good question, Byron. Check Cohen-Mansfield Agitation Inventory, initially developed for people with dementia, measures neuropsychiatric symptoms such as agitation and (verbal) agression. A similar instrument is NPI (Neuro-psychiatric Inventory). It is not exactly what you need but perhaps you can find some clues here.

Thanks so much for all of your responses. I am investigating them all. 

Take a look at David Terman: Theories of Group Psychology, Paranoia, and Rage -

chap. 2 in Strozier, Terman & Jones: The Fundamentalist Mindset. Oxford University Press 2010.