Large-scale human migrations, mostly caused by conflict, continue to occur well-into the 21st century. Probably the largest single movement of people from their country of origin to other locales beyond those borders, as well as within those borders, is occurring in Syria as a direct result of that nation's civil war. It is estimated that as much as half of Syria's prewar population of 23 million has migrated, many to various destinations across Europe as well as to refugee camps along the Syrian borders with Turkey and Jordan. That means that as many as 11 to 12 million Syrians have been uprooted from their homes since the war broke out in 2011, and it is likely many will never return to Syria if and when the ongoing conflict ends.
Other major migrations of the last 15 years have occurred in Iraq (as a result of the 2002 U.S. invasion and subsequent occupation), the Democratic Republic of Congo, where the world's bloodiest and most protracted conflict has resulted in millions dead and millions more displaced, Somalia, where an ongoing conflict between the government and the al-Qaeda-affiliated militant movement al-Shabaab continues, with migrants fleeing the fighting to neighboring countries.
The most persistent and numerous migrations continue to involve the United States, with huge waves of migrants arriving from Mexico and Central America, as well as from other regions of the world. And it is the history of migration towards the United States that is most relevant to questions regarding the impact on the lives of American citizens already living here.
Every American's life is affected, both directly and indirectly, by the enormous number of migrants who arrive every month, mostly through the porous southern border with Mexico. The indirect impact can be felt through federal and state financial commitments for the care and education of migrants, both legal and illegal. The Center for Immigration Studies, for instance, estimates that American taxpayers spend over $4 billion annually for health care for illegal immigrants alone, with that number projected to rise to $8.1 billion annually when many of those who entered the United States illegally are provided amnesty by President Obama. [See this source] The Federation for American Immigration Reform estimates the cost to provide education to unaccompanied minor illegal immigrants at over $761 million annually, paid for by the fifty states [See this source].
So, from a financial perspective, the impact on citizens of illegal immigration alone is considerable, and likely to grow. American taxpayers will be impacted by human migrations for the foreseeable future.
The direct impact of human migrations is more dependent upon the geographic proximity of one's home to the greatest concentrations of migrants. Those who grew up in the American Southwest during the 1960s through the present have seen that region gradually transformed into one more bilingual and multicultural. In fact, very soon, the Southwest will be primarily of Latino heritage. How that will affect those of European and Asian ancestry remains to be seen, but the cultural transformation is substantial. How one adapts to these changes is dependent upon their psychological and cultural orientation. Many are open to these changes, such as the need to be conversant in Spanish to function efficiently, while others are resistant, sometimes violently so.
The history of New York State provides an interesting case study, as it was the gateway through Ellis Island to successive waves of migrants from Europe and Asia for centuries. Those waves, whether from Ireland, China, Italy, or any other place of origin, regularly entrenched themselves in defined communities, often poor and struggling to attain their vision of "the American Dream." Over time, as various ethnicities assimilated and achieved measures of prosperity, they dispersed to suburban communities, their former neighborhoods inhabited by more recent migrations. New York, though, managed to retain its character and continue as an important center of American culture.
Human migrations have occurred throughout history, and have left their imprints on most of the inhabited world. If one were to point to the likeliest flashpoint for future conflicts stemming from the failed assimilation of migrations to new homes, it will involve migrations of Muslims from the Middle East and North Africa to Europe, where European efforts at retaining their unique identities will increasingly clash with the practices and cultures of those from regions with very different customs.