When Is A Tribe Not A Tribe

As we grow up, we were taught that all Jews are descendants of twelve tribes that grew into one mighty nation.
Is this history the truth birth of our nation, or is it historical fiction designed to unify what is not now nor has ever been a truly unified ethnic group?
We are going to explore potential origins of parts of Israel, and suggest when the story was first told, and who had the most to gain by it.