This just isn't true. The US has been a multiracial nation for most of its history due to the country's enormous population of enslaved and eventually emancipat

This just isn't true. The US has been a multiracial nation for most of its history due to the country's enormous population of enslaved and eventually emancipated black people combined with an extraordinarily liberal immigration system. The US's diversity is one of the things that differentiates it from nearly every European country. It's a good thing. You using the Irish as an example is totally bizarre to me because they barely get along with the English (who are mostly also white and Christian). The Troubles were not that long ago and represent a level of political violence between different cultural groups that the US hasn't seen in a very long time.