The United States has long been a nation shaped by immigration, with successive waves of newcomers contributing to its demographic and cultural landscape. From the late 18th century, when Native peoples, European settlers, and enslaved Africans populated the territory, immigration played a central role in the country's growth and development.

During the 19th century, immigration accelerated significantly, particularly as the country expanded westward. Between 1820 and 1860, over five million immigrants arrived, benefiting from relatively open borders and improved transportation such as steamships and expanding rail networks. Political unrest in Europe and events like the Irish famine prompted increased migration from Western Europe after 1840, while the 1848 California gold rush attracted many Asian immigrants, who were often recruited for agricultural and railroad work.

The late 19th and early 20th centuries witnessed a surge of immigrants from Eastern Europe and Italy, driven by pogroms and political changes at home. From 1880 to 1920, an estimated 24 million immigrants entered the United States, settling primarily in northern cities and the Midwest but largely avoiding the South due to established labor structures there. By 1910, immigrants or their children made up the majority of populations in cities including Boston, Chicago, Cleveland, Detroit, and New York City. This influx increased cultural diversity, adding new languages and cuisines, but also led to overcrowded urban areas and fueled fears among some Americans about assimilation and social cohesion.

Federal immigration policy began to shift in the late 19th century with the Chinese Exclusion Act of 1882, the first major law to significantly restrict immigration based on nationality. Subsequent legislation in the 1920s introduced a quota system that heavily favored Western Europeans while limiting entrants from Southern and Eastern Europe and nearly excluding other regions. Although no quotas applied to countries in the Americas and the Caribbean, Mexican immigrants faced mass deportations during the 1930s and 1950s, despite agricultural industries relying heavily on their labor.

For much of the mid-20th century, immigration levels declined, with the foreign-born population reaching historic lows. The children of immigrants absorbed into American society retained cultural traditions, while a nationwide reassessment of immigration policies took shape alongside the civil rights movement. In the 1960s, legislation replaced nationality-based quotas with systems prioritizing family reunification and skilled workers. This change triggered new waves of immigration, including refugees from Southeast Asia displaced by Cold War conflicts.

In more recent decades, immigration from the Western Hemisphere came under restrictions for the first time, leading many migrants to settle permanently in the United States rather than return intermittently. This period also saw a rise in unauthorized immigration due to limited legal pathways. Under the Biden administration, immigration patterns shifted yet again, with steady visa issuance accompanied by large numbers of asylum seekers arriving from Central America and elsewhere, driven by political instability and humanitarian crises in countries such as Cuba, Haiti, Venezuela, Afghanistan, and Ukraine.

Looking ahead, demographic experts suggest the U.S. may soon experience stagnation or decline in net immigration, influenced by tightened enforcement policies enacted during the previous administration and an absence of new comprehensive immigration reforms since the 1980s. Despite this, persistent economic needs and the country’s aging population continue to attract immigrants. The future composition of immigration flows will likely reflect the ongoing tension between labor demands and political resistance, shaping the evolving mosaic of American society.