This is a big question, worthy of a book, actually, but a brief overview is a good starting place. America is a nation founded upon immigration, from its beginnings to the present. Aside from Native Americans, who were present when America began to be settled, we are all immigrants or descendants of immigrants. The consequences of this are a country that is rich in talent, perseverance, and diversity, but which continues to have conflicts and prejudices concerning immigration.
In the earlier years of our country, the metaphor for the United States regarding its immigrants was that it was a "melting pot." Immigrants were encouraged to assimilate into mainstream culture, which was mostly an English and northern European-based culture, as quickly as they could, and most did so quite willingly, because they sought the American Dream and also because they faced tremendous prejudice. There was a time, for example, when there were signs in shop windows saying "No Irish Need Apply." Waves of Italian and Portuguese immigrants faced similar circumstances, as did the enormous influx of eastern Europeans, who were allowed to come when immigration policies expanded in response to the need for labor. At this point in our history, immigration from Latin America and Africa was virtually non-existent. Settlement houses were created to help immigrants learn to speak English, learn to cook the "American" way, and get them melted into the pot. In those days, the influence of immigration was not so much to create diversity as it was to capitalize on the hard work of immigrants and any skills that they brought to their new country. They saved their money, they worked hard, and they made sure their children were educated, but they largely abandoned the cultures they had been born into. I have a dear friend of Italian descent, whose mother was born in Italy, in the 1920's. My friend has always lamented the fact that her mother refused to do any Italian cooking, a good example of the immigrant attitude of those times, when immigrants had a profound influence with their hard work and contributions, but when they gave up to a large degree their cultural identity.
Let's fast forward now to more recent times. Immigration policy has expanded to include people from all over the world, from Latin America, from Africa, from Asia, from India, and from the Middle East. Concomitantly, we have a conflicting metaphor in America, which is the "salad bowl." Many people think that the melting pot is a mistake, that people should not relinquish their cultures when they come here, that we should celebrate the diversity of our immigrant population, more as the vegetables in a salad bowl are a pleasing combination of differences, happily co-existing together. This might not have created a conflict if we had maintained an immigration policy that focused on allowing the English and northern Europeans, since this was largely the prevailing culture here to begin with, but as more and more darker-skinned people, with cultures and religions that Americans perceive to be "alien" have immigrated, there are those whose prejudices cause them to take refuge in the melting pot metaphor, with movements to restrict immigration, with "English only" campaigns, and innumerable other efforts to eradicate diversity in the United States. This has caused a great deal of dissension in the United States, and the electoral politics going on right now are a reflection of this, to allow only Christians from Syria to emigrate, for instance, or to build enormous walls at our borders. During the Ebola crisis, many called for keeping out anyone from an African nation that had Ebola victims. Thus, the influence of immigration has been to create great turmoil in American politics and policy. But the salad bowl metaphor had grabbed hold, giving the United States a wonderfully diverse culture. We have Hindu temples, mosques, Korean churches, Cinco de Mayo, and Chinese New Year, just to name a few contributions to our culture.
No matter what the prevailing metaphor is, though, the influence of immigration has been to create a great country, and the list of contributions is virtually endless. Edison was the offspring of immigrants, as was Alexander Graham Bell, as was Henry Ford. Einstein was an immigrant, as was Tesla, as was Andrew Carnegie. Every business leader, scientist, and entrepreneur we have had in this country has been an immigrant or the offspring of immigrants. There would be no America without them.
