Approximately 41 million people immigrated to the United States of America between the years 1820 and 1957. During this time period, the United States expanded across North America, growing from 23 to 48 states, and the population grew from approximately 10 million people in 1820, to almost 180 million people by 1957. Economically, the U.S. developed from being an agriculturally focused economy in the 1820s, to having the highest GDP of any single country in the 1950s. Much of this expansion was due to the high numbers of agricultural workers who migrated from Europe, as technological advances in agriculture had lowered the labor demand. The majority of these migrants settled in urban centers, and this fueled the growth of the industrial sector.

American industrialization and European rural unemployment fuel migration The first major wave of migration came in the 1850s, and was fueled largely by Irish and German migrants, who were fleeing famine or agricultural depression at the time. The second boom came in the 1870s, as the country recovered from the American Civil War, and the Second Industrial Revolution took off. The final boom of the nineteenth century came in the 1880s, as poor harvests and industrialization in Europe led to mass emigration. Improvements in steam ship technology and lower fares led to increased migration from Eastern and Southern Europe at the turn of the century (particularly from Italy). War and depression reduces migration Migration to the U.S. peaked at the beginning of the 20th century, before it fluctuated greatly at the beginning of the 20th century. This was not only due to the disruptions to life in Europe caused by the world wars, but also the economic disruption of the Great Depression in the 1930s. The only period between 1914 and 1950 where migration was high was during the 1920s. However, the migration rate rose again in the late 1940s, particularly from Latin America and Asia. The historically high levels of migration from Europe has meant that the most common ethnicity in the U.S. has been non-Hispanic White since the early-colonial period, however increased migration from Latin America, Asia and Africa, and higher fertility rates among ethnic minorities, have seen the Whites' share of the total population fall in recent years (although it is still over three times larger than any other group.

Between 1820 and 1957, more than one million documented migrants arrived in the United States from Asia. The migration rate was quite low until the 1850s, but then there was an influx of Chinese migrants to the US, and almost 300,000 people migrated to the US from China by 1884. This migration from China ended abruptly in the 1880s, as a result of the Chinese Exclusion Act of 1882. This act prohibited the immigration of Chinese laborers to the United States, and, despite the fact that it was only intended to last for ten years, it officially remained in effect until 1943, and in practice until 1965.

After this law came into effect, migration from Asia was quite low until the end of the nineteenth century. As the twentieth century began, migration from Asia to the US increased gradually, particularly from Japan and Turkey, although overall migration decreased again following the First World War and the Great Depression. In the lead up to the Second World War, migration to the US decreased greatly, particularly from Japan, who were one of America's enemies during the war. As the Chinese Civil War ended in the late 1940s, the US accepted a few thousand Chinese asylum seekers, and then migration from Asia grew to it's pre-Depression levels in the 1950s.

Following the Second World War and Italian Civil War, European countries became the most popular destination for Italian emigrants. Although France was the most popular destination in the late 1950s, it was replaced by Germany and Switzerland in the 1960s and early 1970s, and the year with the highest level of migration to these three countries was 1961, with more than 300,000 migrants in total.

Between 2008 and 2017, the main destination countries were Germany, the United Kingdom, Switzerland, and France. In 2017, 20.6 thousand Italians emigrated to the United Kingdom.

During the 1950s and 1960s, the population of Eastern Europe grew by approximately 1.3 percent each year, although it varied per country. The Soviet Union and Poland saw the largest growth, with annual increases of 1.5 and 1.4 percent respectively. While most countries saw significant population growth in this period, East Germany's population actually decreased, from 18.4 million in 1950 to 17.1 million in 197. This was due to the high rates of Westward migration in the 1950s, before border restrictions became much more stringent after 1961.

Since the 1950s, the number of forcibly displaced persons recognized by the United Nations has increased drastically; from around 2.1 million international refugees in 1951 to almost 123 million displaced persons in total in 2023. Annual figures are not reflective of the actual number of forcibly displaced people in the world, but rather the number of people identified as such by the UN. Preliminary figures for 2024 show that this figure may now reach the 125 million mark, with major new crises in Sudan and Palestine sending this figure higher, after the Russia-Ukraine War pushed this figure past 100 million people for the first time in 2022. UNHCR The United Nations High Commissioner for Refugees (UNHCR) was founded in 1950 to deal with the large number of displaced persons in Europe in the aftermath of the Second World War. Since then, the scale and geographical scope of its operations has broadened significantly, as it works to provide humanitarian aid, logistical support, and long-term solutions to crises across the globe. The UNHCR played an instrumental role in facilitating or limiting the impact of many decolonization movements across Africa and Asia in the late 20th century, and, in recent decades, it has provided much-needed assistance in conflict areas, such as the Balkans in the 1990s, Afghanistan since the 2000s, and more recently in Syria and Yemen. Alongside the UNHCR, the United Nations Relief and Works Agency (UNRWA) was established in 1949 to provide similar assistance programs for Palestinian refugees and their descendants, and it is currently operational in Jordan, Lebanon, Syria, and the State of Palestine, but its future remains uncertain after the Israeli parliament revoked its license to operate in the country in October 2024. Long-term crises Persistent instability in Sub-Saharan Africa has also been a major area of focus throughout the UNHCR's history, as economic and structural underdevelopment, alongside conflict and political instability, has created several refugee crises that are now in their fourth decade. While countries such as Colombia, Germany, and Turkey have, to varying degrees, successfully managed refugee crises in recent years, the economies of most countries in Sub-Saharan Africa are not equipped to do so. Displacement has placed a great strain on several regions' already-struggling resources, and these are now also being affected by climate change. Countries such as Kenya, Sudan, and Uganda are home to camps or camp networks that house several hundred thousand refugees, with some of the largest in Kenya being established in the early 1990s.

Following the Second World War, Germany was split into four territories, administered by France, the Soviet Union, the United Kingdom and the United States. In 1949, the zones occupied by Britain, France and the US formed the Federal Republic of Germany (West Germany), and the USSR zone became the German Democratic Republic (East Germany). The capital city of Berlin, which was located in East Germany, was also split into two parts, with West Berlin remaining in the Federal Republic of Germany and East Berlin belonging to the Soviet satellite state of the German Democratic Republic. Between 1949 and 1961, over 2.5 million people (mostly skilled laborers) emigrated from East to West Germany in search of economic opportunities and higher standard of living. Increasing restrictions In reaction to this imbalanced migration, the communist East German government increased restrictions on movement to the West, and, despite initial requests being denied by Nikita Khrushchev in 1953, the Soviet leader eventually approved the building of a physical barrier in 1961. Initially, a wire fence was used to separate the East from the West, and this was later reinforced with concrete walls, bunkers, guard towers and landmines, most notably in the case of the Berlin Wall, which became the symbol of German division during the Cold War. From the early 1960s until the late 1980s, migration from East to West Germany dropped significantly. In the 1970s, there was no year where more than 20,000 people moved from the East to West, which is a significant drop from the 1950s, where as many as 331,000 people migrated in 1953 alone. The fall of the iron curtain As the Soviet Union's power weaned in the 1980s, and their influence in Eastern Europe diminished, communism in the Eastern block and Soviet satellite states began to collapse at the end of the decade. On November 9, 1989, when an East German politician mistakenly claimed that restrictions on travel visas would be lifted with immediate effect, thousands of people in Berlin gathered at the checkpoints along the Berlin Wall demanding to be allowed through. As tensions rose, the commanding officers eventually gave in to public demands and opened the barriers, allowing the people to move freely again between both German states. In the days that followed, Germans from both sides of the barrier began to tear down and create holes in the Berlin Wall, in a symbolic act that would represent unity and the end of German division.