In psychology, what matters the most (at least from all of the mentors that I've had in university) is research and potential to do research, so I don't think an IA masters will necessarily increase your chances, other than showing that you have the potential to succeed in a graduate program.
If I were you, I'd look into Peace Psychology programs. I can't think of many off the top of my head, but that sounds like the way that you might want to go, at least within the social psychology field.