Siege Mentality
n
1. (Psychology) A shared feeling of victimisation and defensiveness - a term derived from the actual experience of military defences of real sieges. It is a collective state of mind whereby one believes that one is being constantly attacked, oppressed, or isolated in the face of the negative intentions of the rest of the world.

The result is a state of being overly fearful of surrounding peoples, and an intractably defensive attitude.