The Nativists of the 1850s thought that the Irish and German immigrations had changed American forever—and they had. But the culture was strong enough to absorb the new elements. Plus there was the small distraction of the Civil War. Plus there a West to be won. There was, however, a common faith that bound even as it divided.
The nativists of 1850 had a point, Catholic immigration led to the eventual destruction of America, if you follow demographics as closely as you seem to, then you realize that we don’t exist as “America” by sometime in the near future, for example 2050.
The land will be here, the name will be here, but it will not be what we created, or anything even close to it, or related to it.