Human migration involves the movement of people from one place to another with intentions of settling, permanently or temporarily, at a new location (geographic region). The movement often occurs over long distances and from one country to another, but internal migration (within a single country) is also possible; indeed, this is the dominant form of human migration globally. Migration is often associated with better human capital at both individual and household level, and with better access to migration networks. Age is also important for both work and non-work migration. People may migrate as individuals, in family units or in large groups. There are four major forms of migration: invasion, conquest, colonization and emigration/immigration.
Persons moving from their home due to forced displacement (such as a natural disaster or civil disturbance) may be described as displaced persons or, if remaining in the home country, internally-displaced persons. A person who seeks refuge in another country can, if the reason for leaving the home country is political, religious, or another form of persecution, make a formal application to that country where refuge is sought and is then usually described[by whom?] as an asylum seeker. If this application is successful this person's legal status becomes that of a refugee.
In contemporary times,[when?] migration governance has become closely associated with state sovereignty. States retain the power of deciding on the entry and stay of non-nationals because migration directly affects some of the defining elements of a State.
Depending on the goal and reason for relocation, persons who migrate can be divided into three categories: migrants, refugees, and asylum seekers. Each category is defined broadly as the mixed circumstances might occur and motivate a person to change their location.
As such, migrants are traditionally described as persons who change the country of their residence for general reasons and purposes. These purposes may include the search for better job opportunities or healthcare needs. This term is the most generally defined one as anyone changing their geographic location permanently can be considered migrants.
Contrastly, refugees are not narrowly defined and are described as persons who do not relocate willingly. The reasons for the refugees’ migration usually involve war actions within the country or other forms of oppression, coming either from the government or non-governmental sources. Refugees are usually associated with people who must unwillingly relocate as fast as possible; hence, such migrants will likely relocate undocumented.
Asylum seekers are associated with persons who also leave their country unwillingly, yet, who also do not do so under oppressing circumstances such as war or death threats. The motivation to leave the country for asylum seekers might involve an unstable economic or political situation in the country or high rates of crime. Thus, asylum seekers relocate predominantly in order to escape the degradation of the quality of their lives.
Nomadic movements are normally not regarded as migrations, as the movement is generally seasonal, there is no intention to settle in the new place, and only a few people have retained this form of lifestyle in modern times. Temporary movement for the purpose of travel, tourism, pilgrimages, or the commute is also not regarded as migration, in the absence of an intention to live and settle in the visited places.
The impacts of human migration on the world economy has been largely positive. In 2015, migrants, who constituted 3.3% of the world population, contributed 9.4% of global GDP.
According to the Centre for Global Development, opening all borders could add $78 trillion to the world GDP.
Remittances (funds transferred by migrant workers to their home country) form a substantial part of the economy of some countries. The top ten remittance recipients in 2018.
|Rank||Country||Remittance (in billions of US dollars)||Percent of GDP|
In addition to economic impacts, migrants also make substantial contributions in the areas of sociocultural and civic-political life. Sociocultural contributions occur in the following areas of societies: food/cuisine, sport, music, art/culture, ideas and beliefs; civic-political contributions relate to participation in civic duties in the context of accepted authority of the State. It is in recognition of the importance of these remittances that the United Nations Sustainable Development Goal 10 targets to substantially reduce the transaction costs of migrants remittances to less than 3 percent by 2030.
Migration is usually divided into two categories: voluntary migration and forced migration.
The distinction between involuntary (fleeing political conflict or natural disaster) and voluntary migration (economic or labour migration) is difficult to make and partially subjective, as the motivators for migration are often correlated. The World Bank estimated that, as of 2010, 16.3 million or 7.6% of migrants qualified as refugees. This number grew to 19.5 million by 2014 (comprising approximately 7.9% of the total number of migrants, based on the figure recorded in 2013). At levels of roughly 3 percent the share of migrants among the world population has remained remarkably constant over the last 5 decades.
Voluntary migration is based on the initiative and the free will of the person and is influenced by a combination of factors: economic, political and social: either in the migrants` country of origin (determinant factors or "push factors") or in the country of destination (attraction factors or "pull factors").
"Push-pull factors" are the reasons that push or attract people to a particular place. "Push" factors are the negative aspects of the country of origin, often decisive in people`s choice to emigrate and the "pull" factors are the positive aspects of a different country that encourages people to emigrate in search of a better life. Although the push-pull factors are apparently diametrically opposed, both are sides of the same coin, being equally important. Although specific to forced migration, any other harmful factor can be considered a "push factor" or determinant / trigger factor, such examples being: poor quality of life, lack of jobs, excessive pollution, hunger, drought or natural disasters. Such conditions represent decisive reasons for voluntary migration, the population preferring to migrate in order to prevent financially unfavorable situations or even emotional and physical suffering. 
There exist contested definitions of forced migration. However, the editors of a leading scientific journal on the subject, the Forced Migration Review, offer the following definition: Forced migration refers to the movements of refugees and internally displaced people (displaced by conflict) as well as people displaced by natural or environmental disasters, chemical or nuclear disasters, famine, or development projects. These different causes of migration leave people with one choice, to move to a new environment. Immigrants leave their beloved homes to seek a life in camps, spontaneous settlement, and countries of asylum. 
By the end of 2018, there were an estimated 67.2 million forced migrants globally—25.9 million refugees displaced from their countries, and 41.3 million internally displaced persons that had been displaced within their countries for different reasons. 
Numerous causes impel migrants to move to another country. For instance, globalization has increased the demand for workers in order to sustain national economies. Thus one category of economic migrants - generally from impoverished developing countries - migrates to obtain sufficient income for survival.[need quotation to verify] Such migrants often send some of their income home to family members in the form of economic remittances, which have become an economic staple in a number of developing countries. People may also move or are forced to move as a result of conflict, of human-rights violations, of violence, or to escape persecution. In 2013 it was estimated[by whom?] that around 51.2 million people fell into this category.[need quotation to verify] Other reasons people may move include to gain access to opportunities and services or to escape extreme weather. This type of movement, usually from rural to urban areas, may class as internal migration.[need quotation to verify] Sociology-cultural and ego-historical factors also play a major role. In North Africa, for example, emigrating to Europe counts as a sign of social prestige. Moreover, many countries were former colonies. This means that many have relatives who live legally in the (former) colonial metro pole, and who often provide important help for immigrants arriving in that metro pole. Relatives may help with job research and with accommodation. The geographical proximity of Africa to Europe and the long historical ties between Northern and Southern Mediterranean countries also prompt many to migrate.
The question whether a person takes the decision to move to another country depends on the relative skill premier of the source and host countries. One is speaking of positive selection when the host country shows a higher skill premium than the source country. Negative selection, on the other hand, occurs when the source country displays a lower skill premium. The relative skill premia defines migrants selectivity. Age heaping techniques display one method to measure the relative skill premium of a country.
A number of theories attempt to explain the international flow of capital and people from one country to another.
Recent academic output on migration comprises mainly journal articles. The long-term trend shows a gradual increase in academic publishing on migration, which is likely to be related to both the general expansion of academic literature production, and the increased prominence of migration research. Migration and research on it has further changed with the revolution in information and communication technologies.
Main article: Neoclassical economics
This theory of migration states that the main reason for labor migration is wage difference between two geographic locations. These wage differences are usually linked to geographic labor demand and supply. It can be said that areas with a shortage of labor but an excess of capital have a high relative wage while areas with a high labor supply and a dearth of capital have a low relative wage. Labor tends to flow from low-wage areas to high-wage areas. Often, with this flow of labor comes changes in the sending as well as the receiving country. Neoclassical economic theory is best used to describe transnational migration, because it is not confined by international immigration laws and similar governmental regulations.
Dual labor market theory states that migration is mainly caused by pull factors in more developed countries. This theory assumes that the labor markets in these developed countries consist of two segments: the primary market, which requires high-skilled labor, and the secondary market, which is very labor-intensive requiring low-skilled workers. This theory assumes that migration from less developed countries into more developed countries is a result of a pull created by a need for labor in the developed countries in their secondary market. Migrant workers are needed to fill the lowest rung of the labor market because the native laborers do not want to do these jobs as they present a lack of mobility. This creates a need for migrant workers. Furthermore, the initial dearth in available labor pushes wages up, making migration even more enticing.
This theory states that migration flows and patterns can't be explained solely at the level of individual workers and their economic incentives, but that wider social entities must be considered as well. One such social entity is the household. Migration can be viewed as a result of risk aversion on the part of a household that has insufficient income. The household, in this case, is in need of extra capital that can be achieved through remittances sent back by family members who participate in migrant labor abroad. These remittances can also have a broader effect on the economy of the sending country as a whole as they bring in capital. Recent research has examined a decline in U.S. interstate migration from 1991 to 2011, theorizing that the reduced interstate migration is due to a decline in the geographic specificity of occupations and an increase in workers’ ability to learn about other locations before moving there, through both information technology and inexpensive travel. Other researchers find that the location-specific nature of housing is more important than moving costs in determining labor reallocation.
Main article: Relative deprivation
Relative deprivation theory states that awareness of the income difference between neighbors or other households in the migrant-sending community is an important factor in migration. The incentive to migrate is a lot higher in areas that have a high level of economic inequality. In the short run, remittances may increase inequality, but in the long run, they may actually decrease it. There are two stages of migration for a worker: first, they invest in human capital formation, and then they try to capitalize on their investments. In this way, successful migrants may use their new capital to provide for better schooling for their children and better homes for their families. Successful high-skilled emigrants may serve as an example for neighbors and potential migrants who hope to achieve that level of success.
World-systems theory looks at migration from a global perspective. It explains that interaction between different societies can be an important factor in social change within societies. Trade with one country, which causes economic decline in another, may create incentive to migrate to a country with a more vibrant economy. It can be argued that even after decolonization, the economic dependence of former colonies still remains on mother countries. This view of international trade is controversial, however, and some argue that free trade can actually reduce migration between developing and developed countries. It can be argued that the developed countries import labor-intensive goods, which causes an increase in employment of unskilled workers in the less developed countries, decreasing the outflow of migrant workers. The export of capital-intensive goods from rich countries to poor countries also equalizes income and employment conditions, thus also slowing migration. In either direction, this theory can be used to explain migration between countries that are geographically far apart.
Old migration theories are generally embedded in geography, sociology or economics. They explain migration in specific periods and spaces. In fact, Osmosis theory explains the whole phenomenon of human migration. Based on the history of human migration, Djelti (2017a) studies the evolution of its natural determinants. According to him, human migration is divided into two main types: the simple migration and the complicated one. The simple migration is divided, in its turn, into diffusion, stabilisation and concentration periods. During these periods, water availability, adequate climate, security and population density represent the natural determinants of human migration. For the complicated migration, it is characterised by the speedy evolution and the emergence of new sub-determinants notably earning, unemployment, networks and migration policies. Osmosis theory (Djelti, 2017b) explains analogically human migration by the biophysical phenomenon of osmosis. In this respect, the countries are represented by animal cells, the borders by the semipermeable membranes and the humans by ions of water. As to osmosis phenomenon, according to the theory, humans migrate from countries with less migration pressure to countries with high migration pressure. In order to measure the latter, the natural determinants of human migration replace the variables of the second principle of thermodynamics used to measure the osmotic pressure.
Main article: Sociology of immigration
A number of social scientists have examined immigration from a sociological perspective, paying particular attention to how immigration affects, and is affected by, matters of race and ethnicity, as well as social structure. They have produced three main sociological perspectives:
More recently,[when?] as attention has shifted away from countries of destination, sociologists have attempted to understand how transnationalism allows us to understand the interplay between migrants, their countries of destination, and their countries of origins. In this framework, work on social remittances by Peggy Levitt and others has led to a stronger conceptualisation of how migrants affect socio-political processes in their countries of origin.
Much work also takes place in the field of integration of migrants into destination-societies.
Political scientists have put forth a number of theoretical frameworks relating to migration, offering different perspectives on processes of security, citizenship, and international relations. The political importance of diasporas has also become[when?] a growing field of interest, as scholars examine questions of diaspora activism, state-diaspora relations, out-of-country voting processes, and states' soft power strategies. In this field, the majority of work has focused on immigration politics, viewing migration from the perspective of the country of destination. With regard to emigration processes, political scientists have expanded on Albert Hirschman's framework on '"voice" vs. "exit" to discuss how emigration affects the politics within countries of origin.
Certain laws of social science have been proposed to describe human migration. The following was a standard list after Ernst Georg Ravenstein's proposal in the 1880s:
Lee's laws divide factors causing migrations into two groups of factors: push and pull factors. Push factors are things that are unfavourable about the area that one lives in, and pull factors are things that attract one to another area.
The modern field of climate history suggests that the successive waves of Eurasian nomadic movement throughout history have had their origins in climatic cycles, which have expanded or contracted pastureland in Central Asia, especially Mongolia and to its west the Altai. People were displaced from their home ground by other tribes trying to find land that could be grazed by essential flocks, each group pushing the next further to the south and west, into the highlands of Anatolia, the Pannonian Plain, into Mesopotamia, or southwards, into the rich pastures of China. Bogumil Terminski uses the term "migratory domino effect" to describe this process in the context of Sea People invasion.
The theory that migration occurs because individuals search for food, sex and security outside their usual habitation; Idyorough (2008) is of the view that towns and cities are a creation of the human struggle to obtain food, sex and security. To produce food, security and reproduction, human beings must, out of necessity, move out of their usual habitation and enter into indispensable social relationships that are cooperative or antagonistic. Human beings also develop the tools and equipment to enable them to interact with nature to produce the desired food and security. The improved relationship (cooperative relationships) among human beings and improved technology further conditioned by the push and pull factors all interact together to cause or bring about migration and higher concentration of individuals into towns and cities. The higher the technology of production of food and security and the higher the cooperative relationship among human beings in the production of food and security and in the reproduction of the human species, the higher would be the push and pull factors in the migration and concentration of human beings in towns and cities. Countryside, towns and cities do not just exist but they do so to meet the human basic needs of food, security and the reproduction of the human species. Therefore, migration occurs because individuals search for food, sex and security outside their usual habitation. Social services in the towns and cities are provided to meet these basic needs for human survival and pleasure.
By their very nature, international migration and displacement are transnational issues concerning origin and destination States, as well as States through which migrants may travel (often referred to as “transit” States) or in which they are hosted following displacement across national borders. And yet, somewhat paradoxically, the majority of migration governance has historically remained with individual States, their policies and regulations on migration typically made at the national level. For the most part, migration governance has been closely associated with State sovereignty. States retain the power of deciding on the entry and stay of non-nationals because migration directly affects some of the defining elements of a State. Bilateral and multilateral arrangements are features of migration governance, and there are several global arrangements in the form of international treaties in which States have reached agreement on the application of human rights and the related responsibilities of States in specific areas. The 1966 International Covenant on Civil and Political Rights and the 1951 Convention relating to the Status of Refugees (Refugee Convention) are two significant examples, notable for being widely ratified. Other migration conventions have not been so broadly accepted, such as the International Convention on the Protection of the Rights of All Migrant Workers and Members of Their Families, which still has no traditional countries of destination among its States parties. Beyond this, there have been numerous multilateral and global initiatives, dialogues and processes on migration over several decades. The Global Compact for Safe, Orderly and Regular Migration (Global Compact for Migration) is another milestone, as the first internationally negotiated statement of objectives for migration governance striking a balance between migrants’ rights and the principle of States’ sovereignty over their territory. Although it is not legally binding, the Global Compact for Migration was adopted by consensus in December 2018 at a United Nations conference in which more than 150 United Nations Member States participated and, later that same month, in the United Nations General Assembly (UNGA), by a vote among the Member States of 152 to 5 (with 12 abstentions).
[...] families may assume transnational morphologies with the strategic intent of ensuring economic survival or maximising social mobility.
The proximity of North Africa to southern Europe, the liberal mobility policies of most European countries, and the historical links between northern and southern Mediterranean countries are all key factors encouraging people to migrate to Europe.