Tribalism and silly notions stem from our primitive egos. The primitive ego most hates change and being thought wrong. Thus those, who, for an infinite number of reasons, fail to significantly develop their intellect settle into a conservative state that often leans towards violence and decay.
They are narrow minded, fearful of those unlike their own kind, hate change and explode at those who refuse to validate their reasoning. They watch Fox News and cling to horryfic demagogic leaders — despising those whom build their lives on facts and common sense. They remain tribalistic prisoners of their primitive egos.
And that is how the modern world is divided — those who are ego locked vs those possessing a free intellect.