[gumby]

> > inter-ethnic conflicts among White Americans

The context of the Johnson–Reed Act is more complex than you make it and significantly restricted people you would call “white”, not just other “undesirables”.

Most of the violence of the early 20th century was political (especially, but not only, during WWI, which is the example you chose) and seemingly had more to do with age demographics than racial (a similar problem arose a millennium earlier, driving the invention of crusades). The biggest period was after the Johnson-Reed act, as part of a broader increase in crime.

Yes there was an enormous amount of racial violence, but most of it was directed against black citizens, none of whom were recent immigrants.

I have followed this history because without the 1965 Immigration act I would not have been permitted to come to the US and attend school. And I come from a country with twice the immigration rate of the US, but little violence.