International migration gives rise to problems of assimilation and to the development of ethnic and religious minorities that cannot readily be integrated into the community of their adopted country. Antagonism is likely to develop against migrant groups which are different in appearance, habits and attitudes from the local inhabitants; and to grow in areas where migrants are relatively numerous. Contemporary migration is also marked by the outflow of skills from many developing countries. The problem arises not only with regard to highly skilled professionals; there is also a loss of scarce skills in various sub-professional categories, a type of middle level technical and administrative brain-drain. As a result many developing countries face severe shortages in certain skills and professions

According to ILO surveys, in 1981 there were two million Asian migrant workers abroad, the vast majority of them in the Middle East, and most of them skilled blue collar workers in construction and transport. Pakistan had 775,000 workers abroad in 1982; 354,000 workers left the Philippines in 1982; and 250,000 Indians sought work outside India during that same year. Of the developed countries in 1991, Australia has the highest percentage of its population foreign-born with 20%. Then follow Switzerland (17.2%), Canada (16.2%), France (10.5%), the UK (8.7%) and the USA (6%)
The recent migrations are of a modest scale compared to the mass migrations of population that took place from Europe to the New World in the latter part of the 19th century and the early part of the 20th century. However, they represent a resumption of earlier patterns of international migration. It is estimated that at least 52 million people migrated from Europe to the USA, Canada, Latin America and Oceania between 1840 and 1930, and this amounted to 20% of the population of Europe at the beginning of this period. There has also been a significant change in this pattern of migration from Europe and since 1960 there is a positive net migration to western Europe

The volume and nature of international migratory movements continue to undergo rapid changes. Illegal or undocumented migration and refugee movements have gained particular importance; labour migration of considerable magnitude occurs in all regions. The principal root cause of this large scale contemporary migration is to be found in the disparity in economic development, employment opportunities and living standards between countries at different stages of economic and social development. Natural disasters and political crises are among other principal causes of shifts in migration patterns and the increase in the volume of overall international population movements; though the motivation for most international migration is higher wages. Historically, some migration may have been directly related to population pressure, but today wage differences are the main driving force