Immigration involves moving to a new country with the intention of settling there permanently after leaving one's country of citizenship. In many cases, immigrants go on to become citizens of the receiving nation. Tourists, foreign students, and others who visit or reside in a country temporarily are not considered immigrants. In 2017 the United Nations (UN) Department of Economic and Social Affairs reported a worldwide total of 258 million people living in a country other than the one where they originally held citizenship, including people who immigrated in previous years. The United States has been the world's leading destination for immigrants since 1960. In 2016 the United States hosted nearly 50 million foreign-born residents, including legal permanent residents (LPRs), undocumented immigrants, and naturalized citizens, according to UN estimates. In comparison, the three countries with the next highest foreign-born populations, Saudi Arabia, Germany, and the Russian Federation, are home to 12 million migrants each. Foreign-born residents, however, account for less than 15 percent of the US population, while more than half of the populations of several Middle Eastern countries, including the United Arab Emirates, Kuwait, Qatar, and Bahrain, are foreign-born.

Mexicans make up the largest segment (12.7 million or 25.4 percent) of all immigrants currently living in the United States. In 2013, however, the number of migrants, including temporary visa holders and students, arriving annually from China (147,000) and India (129,000) surpassed the number of people arriving from Mexico (125,000). Immigration records since 2000 suggest this trend will continue with the number of Mexican immigrants decreasing while the number of people arriving from India and China continues to grow. In the twenty-first century, violence and instability in Afghanistan, Myanmar, South Sudan, Syria, and Venezuela have increased the global refugee population, which refers to displaced people forced to leave the country where they live out of concerns for their freedom and safety. About half of the refugees who entered the United States in 2016 came from the Democratic Republic of the Congo, Syria, and Myanmar. The potential benefits of immigration to the immigrant and the host country are compelling, but some people in the United States have expressed concern about the number of people coming to resettle. Though much of the debate has focused on curbing illegal immigration, efforts within the presidential administration of Donald Trump have also tried to reduce legal immigration and refugee admissions to the United States. The Trump administration's hardline approach to immigration has met with protest from politicians and activists who have accused the administration of violating the US Constitution and international human rights legislation with policies that target people from specific religious backgrounds and separate undocumented immigrants, including children, from their families.

Motivations and Impact

People may choose to emigrate, or leave their countries of origin to reside elsewhere, because they face untenable challenges in their home country. Some migrants come to the United States fleeing religious or political persecution or escaping dangerous circumstances, such as war or criminal violence. In such situations, prospective migrants may apply to enter the country as refugees or political asylum grantees. Obtaining such recognition, however, requires extensive vetting, and the process can take several years. Others come to the United States for the purposes of economic migration; they may be attracted by the country's business-friendly culture or seek to pursue high-paying jobs. Whereas many immigrants to the United States were historically drawn by the country's fertile land and industrial advances, economic migrants of the twenty-first century have sought opportunities in many areas, including computer technology, construction, education, agriculture, manufacturing, and domestic work, including childcare and housekeeping. In 2017 immigrants accounted for 17.1 percent of the total US workforce, according to the US Department of Labor's Bureau of Labor Statistics. Immigrants also come to the United States for reasons related to social migration, such as to reunite with family members who immigrated previously, to seek a more tolerant society, or to begin a new family married to a US citizen.

Origin countries are affected when large portions of their populations decide to resettle somewhere else. The outflow of talented, industrious people has led to informal diagnoses of "brain drain," which contend that the origin country suffers from losing valued members of its citizenry. The economies of many origin countries, however, benefit from remittances, money sent by immigrants to their family members after securing employment in the destination country. The World Bank estimates that over $66 billion left the US economy in the form of remittances in 2016.

The impact of immigration on receiving countries has stirred debate among those who feel that immigrants enhance a local population and those who view immigrants as a threat. Though most people in the United States can trace their ancestry beyond the country's borders, public opinion regarding immigration is generally split along partisan lines. Liberals tend to view immigration as a net benefit, noting that most immigrants pay taxes, work jobs that native-born Americans may be unable or unwilling to perform, and enrich their local communities. Conservatives have typically expressed more suspicions, citing concerns that immigrants take jobs away from US citizens and take advantage of government services. Right-wing media outlets have been accused of sensationalizing stories involving immigrants, promoting the idea that immigrants contribute to such social problems as crime and disease, even though studies have indicated that immigrants are less likely to engage in criminal behavior than native-born citizens. Since the September 11, 2001, attacks on the United States, immigrants from Muslim-majority countries have faced increased scrutiny for potentially harboring extremist beliefs or maintaining ties to terrorist organizations.

Historical Immigration in the United States

As the United States emerged from former British colonies populated by European settlers, African slaves, and their descendants, migration to North America has been central to the character of the nation. Shortly after securing independence from Great Britain, the United States passed the Naturalization Act of 1790, the country's first immigration law, which applied only to white people and required individuals to live in the country for two years in order to be naturalized. Though the residency requirement changed through subsequent legislation, the first significant change occurred in 1868 when Congress passed the Fourteenth Amendment, which extended citizenship to anyone born in the United States, including former slaves. The federal government extended naturalization rights through the Naturalization Act of 1870 but only to African immigrants, establishing legal justification for denying the option of citizenship to non-white immigrants who were not from Africa.

In 1882 the federal government passed the Chinese Exclusion Act, which banned all Chinese workers from entering the United States until its repeal in 1943. This law was the first and only time the federal government banned the population of an entire country from entry outside of wartime until President Donald Trump proposed travel bans on seven Muslim-majority nations in 2017. The Chinese Exclusion Act reflected a growing concern among some Americans that immigration needed additional regulation. During the late nineteenth century, Congress also passed legislation banning convicted criminals, sex workers, the mentally ill, and migrants deemed incapable of caring for themselves.

As immigrants arrived from an increasingly diverse set of origin countries, some Americans voiced their anxieties that the demographics of the country would change. These concerns led to further restrictions on immigration, including the imposition of literacy requirements through the Immigration Act of 1917 and national quotas as part of the Emergency Quota Act of 1921 and the Immigration Act of 1924, commonly referred to as the Johnson-Reed Act. Together with the Great Depression and the Second World War, these laws sharply limited immigration to the United States in the 1930s and early 1940s.

Reduced immigration contributed to labor shortages, particularly on farms in western states. Because immigration from Latin American countries, including Mexico, was not restricted under the Johnson-Reed Act, immigration from those countries increased in the years subsequent to the law's passing. In 1942, months after Mexico joined the United States in declaring war on Germany, Italy, and Japan, the two countries came to an agreement in which the Mexican government would send agricultural workers to the United States, which led to Congress creating the Bracero Program the following year. As part of the agreement, Mexican workers filled vacancies created when the native-born labor force left to fight in the war. After the war ended and soldiers returned to civilian life, US president Harry Truman commissioned a report on the effects of migrant labor that concluded the Bracero Program, as well as a wave of illegal immigration that accompanied it, had hurt the hireability and earning power of native-born workers. In response to the report, the administration of Truman's successor Dwight Eisenhower proposed sanctions on employers who hired undocumented immigrants, and launched an initiative to deport millions of Mexicans with the offensive yet official designation Operation Wetback. Many of these deportees had originally entered the United States through the Bracero Program.

Following calls for reform to immigration law, the nationality quota system was abolished as part of the Immigration and Naturalization Act of 1965. The law replaced the quota system with a preference system favoring skilled workers and relatives of US citizens and resident aliens. Immigration from Asia, Africa, and Latin America increased in subsequent decades as a result. Following the US withdrawal of armed forces in Vietnam in 1975, Congress amended existing immigration legislation with the Refugee Act of 1980, which revised the government's definition of a refugee to align with the UN definition and enabled a greater number of refugees from Vietnam and other war-torn countries to resettle in the United States than had previously been allowed. The presidential administration of Ronald Reagan addressed concerns about illegal immigration through the Immigration Reform and Control Act of 1986, which imposed penalties on employers who hired undocumented immigrants and created a path to amnesty for undocumented immigrants without criminal records who had entered the country before 1982. Reforms passed during the 1990s expanded the Immigration and Natural Act of 1965 to allow more legal immigration while also addressing concerns about illegal immigration and criminal behavior among legal immigrants.

Several immigration laws were proposed and enacted in the early twenty-first century in response to security concerns following the September 11, 2001, terrorist attacks as well as concerns about illegal immigration. In 2002 the federal government approved state and local police cooperation with federal immigration enforcement efforts through 287(g) agreements, which were originally proposed as part of the Illegal Immigration Reform and Immigrant Responsibility Act of 1996. In addition to the threat of terrorism, lawmakers sought to address the plight of undocumented immigrants and the effects of illegal immigration on US society. In 2001 lawmakers first introduced the Development, Relief and Education for Alien Minors (DREAM) Act, which aimed to provide legal immigration status to undocumented immigrants who had been brought to the United States as children. Though the law has been introduced on several occasions, it has never passed. In 2012, however, the US Department of Homeland Security (DHS) under the presidential administration of Barack Obama created the Deferred Action for Childhood Arrivals (DACA) policy, which authorized such undocumented immigrants to work legally and deferred deportation if the immigrant remained in good legal standing. Nearly 800,000 immigrants obtained DACA status, allowing them to work and attend school legally. In 2017, however, the DHS under the Trump administration announced its intentions to end the DACA program and has only continued to renew applications to comply with a federal court order issued in April 2018. Though the creation of DACA helped many undocumented immigrants, Obama received a negative reputation among many immigration activists for continuing previously established programs that resulted in over 500,000 deportations. Obama also faced criticisms from conservatives who felt his policies encouraged illegal immigration.

Legal Immigration Issues

People who intend to legally immigrate to the United States must apply for a visa at a US consulate or embassy. The application process includes an interview, criminal background check, review of financial information, and a medical examination. Applicants also require sponsorship from a US citizen or legal permanent resident, typically a relative or employer. Aspiring immigrants who lack specific, in-demand work skills or who are not immediate relatives of a legal US resident may apply through the Diversity Immigrant Visa Program, which provides as many as 50,000 visas each year through a lottery system to residents of countries with low rates of immigration. Such applicants must submit a new petition each year, and many wait years before receiving a visa. Those fleeing dangerous situations or persecution can also apply for asylum or refugee status.

These preferences have faced several criticisms, spurring calls for reform. Providing visas to the immediate family members of legal US residents, commonly referred to as family reunification, has drawn condemnation from critics, including President Donald Trump, who worry that such preferences will lead to an endless supply of immigrants, citing fears of "chain migration," without evidence to support their claims. The law actually limits family reunification preferences to the spouses, parents, or the unmarried children of a legal permanent resident.. Further criticisms against family reunification maintain that the preference encourages the immigration of people who may lack formal education or practical job skills. Many cultures, however, including the United States, place a high value on family relationships. Family-sponsored immigration accounts for the largest portion of successful applicants. According to the DHS Yearbook of Immigration Statistics, 238,087 immigrants obtained legal permanent resident status through family-sponsored preference in FY2016, 137,893 immigrants obtained their status through employment-based preference, and 157,425 immigrants obtained either refugee status or asylum that same year. While some critics have urged a reduction in the number of legal immigrants allowed into the country, advocates for maintaining or increasing the amount of legal immigration contend that doing so discourages illegal immigration. Such advocacy also recognizes the cultural and economic contributions of the US immigrant population.

In 2018 the US Citizenship and Immigration Services (USCIS) created a new office to investigate naturalized citizens and legal permanent residents who may have misrepresented themselves on their immigration applications. If the office believes someone has violated federal law by providing false information, a recommendation is made to the DOJ to have a judge review the person's situation. If the judge finds that the person fabricated information, the person could have their status revoked and be deported. Prior to the 2018 initiatives, civil denaturalization processes rarely took place, typically in cases where the suspect was revealed to be a war criminal attempting to evade justice. The policy of investigating a person's immigration status after they have become naturalized citizens has caused anxiety among many legal immigrants and their families.

Illegal Immigration Issues

In the twenty-first century, illegal immigration continues to be a focus of contention in the United States. Many native-born citizens acknowledge the contributions of undocumented immigrants and believe these people should be afforded the opportunity to obtain legal status. Some jurisdictions, known as sanctuary cities, have adopted policies that limit local law enforcement cooperation with immigration enforcement. The philosophy behind sanctuary cities maintains that such policies improve community safety and that residents are more willing to cooperate with local law enforcement when the threat of deportation is removed. Opponents of sanctuary cities, however, worry that sanctuary policies could make cities more attractive to criminal elements. In a 2017 study of crime in sanctuary cities, researchers from Highline College and the University of California, Riverside, determined that sanctuary cities did not experience higher levels of violent crime, rape, or property crime.

Donald Trump made curbing illegal immigration a central focus of his 2016 presidential campaign, beginning with his initial announcement in which he ridiculed the US immigration system and described Mexican immigrants as criminals, drug traffickers, and rapists. Throughout the campaign and his presidency, Trump has promised to build a wall along the US–Mexico border and proposed various strategies to fund the wall, including a suggestion that the Mexican government pay for its construction, which Mexico has indicated it will not do. During his first month as president, Trump issued several controversial executive orders related to illegal immigration, including a call to increase border security, a condemnation of sanctuary cities, and an entry ban on citizens from seven Muslim-majority countries. Additionally, the administration called for a reduction in legal immigration in August 2017.

The president enlisted many individuals with hardline anti-immigration views to join his administration, including Attorney General Jeff Sessions, Chief of Staff John Kelly, and Senior Policy Advisor Stephen Miller. In April 2018 Sessions notified US attorneys in states along the US–Mexico border that the DOJ was adopting a zero-tolerance policy for attempted illegal entry into the country. This policy required that migrants attempting to enter the United States would be held in custody in a federal facility and face trial before a federal judge. While crossing the border illegally constitutes a federal crime, previous administrations made a practice of releasing families until their cases could be heard because the law forbids the detention of a child in a federal jail. Under the zero-tolerance policy, adults have been sent to federal holding facilities and separated from their children who have been placed in detention centers. As media reports began to reveal the impact and extent of the policy, many Americans, including several Republicans, voiced their opposition. Following political pressure, including a statement that "she hates to see children separated from their families" by First Lady Melania Trump, the president signed an executive order on June 20, 2018, calling for an end to the practice of separating families but not the policy of detaining immigrants. Many politicians criticized the executive order as ineffective. After being ordered by a federal court to reunite the families that had been separated, government agencies struggled to match parents to children. In addition to humanitarian concerns, the imposition of zero tolerance immigration policy faced criticisms for the high costs of detaining and then reuniting families.