Where do you get your numbers? According to this site:

http://www.cis.org/articles/2002/back1302.html

As of 2002, the total of all immigrants, legal and illegal, from all countries, is 33.1 million. They comprise 11.5% of the total population, which is the highest level in 70 years, but still shy of the all-time high of 14.8% in 1890. Basically the 2002 level was the same as the 1930 level.

Did the country collapse? Did the culture collapse? No, but it arguably became more diverse. Which imho isn't a bad thing. I like the fact that I can get decent enchiladas at umpteen different places within 15 minutes of my house. I like the fact that Italian food is now a "staple" genre that's ubiquitously available. I like the fact that I can buy a Shwarma from a middle-eastern guy, or Thai food from a Thai. Yay multiculturalism.