Illegal immigration is the migration of people into a country in circumstances where such people do not meet the legal requirements for immigrating in that country, that is, when they are violating the immigration laws of that jurisdiction. Illegal immigration has numerous and complex causes, but in general, it consists in people from poor countries seeking better life opportunities in more developed countries. Illegal immigration has impact on many political, economical, social and ethical issues.
The net flow of illegal immigration pattern is almost entirely from countries of lower socioeconomic levels to countries of higher socioeconomic levels, and particularly from developing countries to developed countries. While there are other causes associated with poorer countries (described below), the most common motivation for illegal immigrants is the pursuit of greater economic opportunities and quality of life in the destination state.
Under the basic cost/benefit argument for illegal immigration, potential immigrants believe the probability and benefits of successfully migrating to the destination country are greater than the costs. These costs may include restrictions living as an illegal immigrant in the destination country, leaving family and ways of life behind, and the probability of being caught and resulting sanctions. Proposed economic models, based on a cost/benefit framework, have varying considerations and degrees of complexity.
The neoclassical economic model looks only at the probability of success in immigrating and finding employment, and the increase in real income an illegal immigrant can expect. This explanation would account for the economies of the two states, including how much of a "pull" the destination country has in terms of better-paying jobs and improvements in quality of life. It also describes a "push" that comes from negative conditions in the home country like lack of employment or economic mobility.
Neoclassical theory also accounts for the probability of successful illegal emigration. Factors that affect this include as geographic proximity, border enforcement, probability and consequences of arrest, ease of illegal employment, and chances of future legalization. This model concludes that in the destination country, illegal workers tend to add to and compete with the pool of unskilled laborers. Illegal workers in this model are successful in finding employment by being willing to be paid lower wages than native-born workers are, sometimes below the minimum wage. Economist George Borjas supports aspects of this model, calculating that real wages of US workers without a high school degree declined by 9% from 1980-2000 due to competition from illegal immigrant workers.
Large scale economic evidence supports neoclassical theory, as may be seen in the long-term correlation of relative wages/unemployment and illegal immigration from Mexico to the US. However, immigration scholars such as Gordon Hanson and Douglas Massey have criticized the model for being oversimplified and not accounting for contradictory evidence, such as low net illegal immigration from Mexico to the US before the 1980s despite significant economic disparity. Numerous refinements have been suggested to account for other factors, as seen below.
In recent years, developing states are pursuing the benefits of globalization by joining decline to liberalize trade. But rapid opening of domestic markets may lead to displacement of large numbers of agricultural or unskilled workers, who are more likely to seek employment and a higher quality of life by illegal emigration. This is a frequently cited argument to explain how the North American Free Trade Association may have impoverished Mexican farmers who were unable to compete with the higher productivity of US subsidized agriculture, especially for corn. NAFTA may have also unexpectedly raised educational requirements for industrial jobs in Mexico, since the new maquiladoras produced export products requiring skills and education that many unskilled workers did not have.
Douglas Massey argues that a bifurcating labor market in developed nations creates a structural demand for unskilled immigrant labor to fill undesirable jobs that native-born citizens do not take, regardless of wages. This theory states that postindustrial economies have a widening gap between well-paying, white-collar jobs that require ever higher levels of education and "human capital", which native-born citizens and legal immigrants can qualify to take, and bottom-tier jobs that are stigmatized and require no education. These "underclass" jobs include harvesting crops, unskilled labor in landscaping and construction, house-cleaning, and maid and busboy work in hotels and restaurants, all of which have a disproportionate number of illegal workers.
Since the decline of middle-class blue-collar jobs in manufacturing and industry, younger native-born generations have chosen to acquire higher degrees now that there are fewer blue-collar careers that a worker with no formal education can find. The majority of new blue-collar jobs are the "underclass" work mentioned above, which suffer from unreliability (i.e. temporary jobs versus a career in a factory), subservient roles, and, critically, a lack of potential for advancement. At the same time, entry-level white-collar and service jobs are much more appealing. These they offer advancement opportunities for native-born workers to enter the dominant educated class, even if they currently pay the same or less than manual labor does.
Hence, this theory holds that in a developed country like the US, where now only 12% of the labor force has less than a high school education, there is a lack of native-born workers who have no choice but to take undesirable manual labor jobs. Illegal immigrants, on the other hand, have much lower levels of education (about 70% of illegal workers in the US from Mexico lack a high school degree). They are still willing to take "underclass" jobs due to their much higher relative wages than those in their home country. Since illegal immigrants often anticipate working only temporarily in the destination country, the lack of opportunity for advancement is less of a problem. Evidence for this can be seen in one Pew Hispanic Center poll of over 3,000 illegal immigrants from Mexico in the US, which found that 79% would voluntarily join a temporary worker program that allowed them to work legally for several years but then required them to leave.
While economic models do look at relative wealth and income between home and destination countries, they do not necessarily imply that illegal migrants are always impoverished by standards of the home country. The poorest classes in a developing country may lack the resources needed to mount an attempt to cross illegally, or the connections to friends or family already in the destination country. Studies from the Pew Hispanic Center have shown that the education and wage levels of illegal Mexican immigrants in the US are around the median for Mexico, and that having family who have emigrated or being from a community with many emigrants is a much better predictor of one's choice to emigrate.
Population growth that exceeds the carrying capacity of an area or environment results in overpopulation. Spikes in human population can cause problems such as pollution, water crisis, and poverty. World population has grown from 1.6 billion in 1900 to an estimated 6.7 billion today. In Mexico alone, population has grown from 13.6 million in 1900 to 107 million in 2007.
In 2000, the United Nations estimated that the world's population was growing at the rate of 1.14% (or about 75 million people) per year. According to data from the CIA's 2005–2006 World Factbooks, the world human population currently increases by 203,800 every day. The United States Census Bureau issued a revised forecast for world population that increased its projection for the year 2050 to above 9.4 billion people, up from 9.1 billion people. We are adding a billion more every 12 years. Almost all growth will take place in the less developed regions.
Some illegal immigrants enter a country legally and then overstay or violate their visa. For example, most of the estimated 200,000 illegal immigrants in Canada (perhaps as high as 500,000), are refugee claimants whose refugee applications were rejected but who have not yet been ejected from the country.
A related way of becoming an illegal immigrant is through bureaucratic means. For example, a person can be allowed to remain in a country - or be protected from expulsion - because he/she needs special pension for a medical condition, deep love for a native, or even to avoid being tried for a crime in his/her native country, without being able to regularize his/her situation and obtain a work and/or residency permit, let alone naturalization. Hence, categories of people being neither "illegal" immigrants nor legal citizens are created, living in a judicial "no man's land". Another example is formed by children of foreigners born in countries observing jus soli ("right of territory"), such as was the case in France until 1994 and in Ireland until 2005. In these countries, it was possible to obtain French or Irish nationality (respectively) solely by being born in France before 1994 or in Ireland before 2005 (respectively). At present, a French born child of foreign parents does not automatically obtain French nationality until residency duration conditions are met. Since 1 January 2005, a child born in Ireland does not automatically acquire Irish nationality unless certain conditions are met.
Many countries have had or currently have laws restricting immigration for economic or nationalistic political reasons. United Nations Security Council Resolution 1373 concerning counter-terrorism, enacted in October 2001, requested of UN member states to restrict immigration laws. Whether a person is permitted to stay in a country legally may be decided by quotas or point systems or may be based on considerations such as family ties (marriage, elderly mother, etc.). Exceptions relative to political refugees or to sick people are also common. Immigrants who do not participate in these legal proceedings or who are denied permission under them and still enter or stay in the country are illegal immigrants, as well as people born on national territory (henceforth not "immigrants") but who have not obtained nationality of their birthplace and have no legal title of residency.
Most countries have laws requiring workers to have proper documentation, often intended to prevent or minimize the employment of unauthorized immigrants. However the penalties against employers are often small and the acceptable identification requirements vague and ill-defined as well as being seldom checked or enforced, making it easy for employers to hire unauthorized labor. Unauthorized immigrants are especially popular with many employers because they can pay less than the legal minimum wage or have unsafe working conditions, secure in the knowledge that few unauthorized workers will report the abuse to the authorities. Often the minimum wages in one country can be several times the prevailing wage in the unauthorized immigrant's country, making even these jobs attractive to the unauthorized worker.
In response to the outcry following popular knowledge of the Holocaust, the newly-established United Nations held an international conference on refugees, where it was decided that refugees (legally defined to be people who are persecuted in their original country and then enter another country seeking safety) should be exempted from immigration laws. It is, however, up to the countries involved to decide if a particular immigrant is a refugee or not, and hence whether they are subject to the immigration controls.