The U.S technological prowess --basically the reason they are able to stand on every other nations shoulders today is roughly because of the mass immigration of German and Japanese scientists , technicians etc etc. after WW2 . Since then continued immigration of skilled personnel in various fields like Engineering , Medicine first from the European Shambles left behind after WW2 and subsequently from myriad impoverished countries (at that time ) like India , China , South East Asian countries even the Phillippines etc etc has created a self sustaining ecosystem whereby since the last 4-5 decades they are able to simply watch technological growth happening only keeping a check on financial ,energy etc security and keeping their governance clean of the plague of unnecessary bureaucratic hinderances and the all pervasive stench of Corruption to quite an extent.
This coupled with a strong and successful state policy involving the idea of "pre-emptive action" in matters of military threats or energy security has led to a state where their progress and prosperity has been , for the most part --quite smooth.
The U.S is no single ethnicity marvel ---Anglo Saxon or otherwise , which might possibly be the reason why immigration is "celebrated" as some commentators and analysts put it.
Its immigration of skilled personnel even in the 21st century that actually stops them from stagnating.
Hence no immigrant needs to be unduly grateful to a land that is basically a land of "immigrants" , so multicultural that it may not be accurately described as having a "distinctive" culture per say.
As long as immigrants remain committed to a state of cultural harmony , understand their roles and duties in society and integrate with the system ( the US society allows a tremendous amount of individual freedom and opportunities for growth once these conditions are met) , they should do just fine.
The only downside is due to the numerical superiority of U.S citizens of Anglo -Saxon heritage , sometimes another ethnic groups cultural sensitivities are misconstrued as "Un-American" .
Also the "racism" problem and the fact that the Rich -poor divide somehow tends to find African -Americans /Mexicans and a few ethnicities on the "poor" side of the dividing line --gives rise to a false impression or prejudice of incapability or lack of intelligence based on Race and thus shapes mainstream social opinion which is sometimes deep rooted and therefore difficult to dislodge.
The analogy may also be applied to the idea of "machismo" , where certain ethnicities especially South Asian ones are supposedly physically weaker and therefore incapable of strenuous jobs reflected most notably in the absence of such ethnicities in sports like baseball , American football, Basketball etc popular in mainstream American society --again giving rise to an erroneous perception of fraility in certain ethnicities.