David Emmons, professor emeritus of history at the University of Montana has argued for decades that the United States made "Irish" and made "Italians." You come to the United States and instead of being from Cork or Milan, you're Irish and Italian. Myself and others have made that observation about Mexico, as well - that traveling to the United States for work in the 1940s contributed to the hardening of a national identity in Mexicans in competition with the regional identity: in Mexico you may be Tapatio or Chilango, but in the US you are Mexican. Again, I only say contributed to the process of a hardening national identity that I think we can trace back to the US invasion and other incursions of Mexican sovereignty by European powers.
At any rate, the folks in the popular media are wrapping their head around ethnicity and race as constructed ideas, and National Public Radio just ran a piece about the growth of Hispanics in the United States. What may have changed is not the number of Hispanics but the number of people self-identifying as Hispanic. In on example from the piece, NPR mentions that first generation Hispanics may self-identify as white while their children will identify as Hispanic because of the construct of race they have received in the US. Read (or listen) to more, here.