Internal migration refers to people within a country moving to another location within its borders, whereas external migration, also known as international migration, refers to the act of migration across borders from one country to another. Usually, the motivations for internal and external migration differ.
The reasons for internal migration are often educational or economic. For example, in the 19th century, many people migrated from the east coast to the west coast of the United States to take advantage of economic opportunities. External migration happens for educational or economic reasons as well, but often, it is politically motivated. International migrants are sometimes refugees or asylum seekers fleeing war, natural disasters, religious or political discrimination. Temporary external migrants move for only a fixed period of time, such as a work contract, program of study or cessation of an armed conflict. Permanent external migrants plan to obtain citizenship or at least gain permanent residency in the country to which they move.
International migration has a profound effect on the societies and economies of the affected countries. Many national and international agencies deal with migration issues, including the International Organization for Migration, the International Network on Migration and Development and the United Nations High Commissioner for Refugees. According to a U.S. State Department citing of U.N. statistics, there were 244 million migrants worldwide, which adds up to more than 3 percent of the world's population.