That assimilatative force is being diluted with all this garbage about "multiculturalism." By definition, America is a polyglot culture, but it works because it's a melting pot. All cultures subsume to the whole, which is then all things yet no one thing in particular.
Today, the tendency is to think of each culture separately -- the hyphenated American -- and to treasure each culture as a whole in itself. That interrupts the process of assimilation, breeds discontent, and exaggerates differences instead of identifying commonalities. It is a wall-building mentality, and must be defeated if the normal cultural dynamics are to apply.
One place we can preserve it is in our language. We decidedly do NOT hablamos Espanol!
The difference between other waves of immigration is the fact that in order to survive here, people HAD to learn English. I don't remember my German grandparents telling me that they could vote in German, get government assistance for free(and in German.) The difference in this wave is that there are NO incentives for learning English becauses everything needed to survive is required by government to be in other languages, right up to having translators required where health care is given.
My birth town was almost pure Swedish until the 1950's, in fact they used to have a sign saying Willkommen, my dad who is of German and Choctaw ancestry caused quite the scandal when he married my mom who was from this town.
English is becoming the language of the whole world. That long term trend will overwhelm any short term imbalance of immigrants not learning English.
The numbers of illegal aliens crossing our borders are swamping the system ... these aren't pockets of legal immigrants, such as the Irish, Italian, Germans, Poles that arrived here & whose arrival was spread out over most of this nations history ... these are hordes, numbers reaching into the millions annually, mostly Spanish speaking from Mexico, Central America, South America that will, in very short order, turn the U.S. into just another Latin American country. Southern CA, Arizona, Texas, New Mexico and Colorado will be the first states to succumb to this onslaught.
I applied for the LAPD back in 1996 and the reason I know that I was not hired is because I was North Carolina and really never dealt with people of other races or their languge. I knew limited spanish growing up in San Antonio where they taught it from Kindergarten but that was it.
I was turned down for a 5 1 Korean woman who wore a skirt that you could tell her religion instead of me.