After the Civil War, as large numbers of non-Anglo / non-Protestant / non-Christian European immigrants began arriving in the country, the conservative elements of this country grew alarmed that "their" country was being taken away from them.
Asian immigrants and their descendants born in the U.S. were denied citizenship for decades and in many cases had their citizenship rights retroactively revoked.
The unholy alliance of wealth + politics + religion (which in truth is always present in all societies to some shape or fashion) became increasingly focused on conservative white male Protestant / Christian values.
Each segment became a circle in an overlapping Venn diagram of prejudice and bigotry. Christians of all stripes were aligned against non-Christians (which included a number of progressives and free thinkers). White Christians were aligned against non-white Christians, Protestants against Catholics. Rural families were aligned against urban families.
Poor people…well, those in charge took care not to let them get aligned against the rich by siding too much with the progressives and free thinkers who made up labor unions; poor people were separated into poor whites and poor blacks and aligned against one another even though they had more in common with each other than with the oligarchs who ran the country.
All vicious circles in one big ugly Venn diagram, and where they overlapped they didn’t merely add on their toxicity, they multiplied it.
And chained together, these vicious circles fed off of each other, reinforced each other, validated each other…
In the post-Civil War era this required a great narrowing of religious attitudes among the dominant white culture. Literalism was brought back to deny scientific evidence that there were no significant differences among people regardless of race / ethnicity / gender / orientation and once immediate handicaps were accounted for, no significant difference between the able and the disabled in terms of their humanity. Moralists decried the use of alcohol and drugs by non-whites and non-Protestants, "negro jungle music", and Hollywood movies (i.e., made by Jews).
It was then and now an attempt to shout down other voices with other histories and experiences. So long as only the dominant culture could present its version of events, they never had to seriously face the consequences of their actions and their ancestors' actions. Whatever problems occurred in society were caused by them not us.
[2/1] Many of them fleeing the same kind of exclusionary practices in Europe that Anglo-Americans were directing against non-whites in America.
[2/2] And, oh, the irony; had they but asked the Native Americans and the Mexican-Americans who had been living on the land since before the first Anglo-European colonists arrived...
[2/3] Many Protestants then and now exclude Catholics from their ranks, but those that do try to gloss over all the significant differences between Roman Catholicism / Eastern orthodox / European Protestantism in order to further their own personal goals.