Your tribe is the set of all people that (a) you consider to be part of your tribe and (b) who consider you to be part of their tribe.

This isn’t a theoretical construct. You can actually enumerate your tribe members from your social graph.

Exercise: to what extent does your tribe correspond to national borders?

Author of The Network State.
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Would you agree that your tribe is also an unofficial and unmapped set of individuals below dunbars number? These people influence you either directly or subliminally 

you may not even speak to them but they do affect your world view by proxy of just being around (the subliminal influencers are often geo constrained)