“I ran across the fact that in 1860 a majority of the inhabitants of WI were foreign-born”
They certainly were, but the difference is that the ‘foreign-born’ cited came from countries that had their foundation in European cultural values and philosphy.
That is certainly not the case now.
Well, yes it is.
Unless Spain is not considered part of Europe. No reasonable person will determine that Spanish-American countries don't have their (primary) foundation in Spanish "cultural values and philosophy."
Now you can make quite a decent case that Spain is a special case in Europe, with its culture dramatically impacted by Muslim conquest and occupation. Although a Spaniard of the time would likely have killed you for saying so.
But Spain is still part of Europe, and Latin American countries are all more European than native in their culture, though the mix varies.
And I have yet to see anybody point out why an individual Mexican peasant in 2012 is inherently less capable of assimilation than a Sicilian peasant in 1912. Both were culturally dramatically different from the American mainstream.
In the early 20s the rate of immigration fell off a cliff, and in the next half-century the immigrants pretty thoroughly assimilated, being isolated from cultural influences from the mother country.
I see no reason the same couldn't be done today, except that our elites won't allow another hiatus in massive immigration.