Internal migration or domestic migration is human migration within a country. Internal migration tends to be travel for education and for economic improvement or because of a natural disaster or civil disturbance, though a study based on the full formal economy of the United States found that the median post-move rise in income was only 1%. Cross-border migration often occurs for political or economic reasons. A general trend of movement from rural to urban areas, in a process described as urbanisation, has also produced a form of internal migration. History Many countries have experienced massive internal migration. The United States has experienced the following major migrations: A massive internal migration from the eastern states toward the west coast during the mid-19th century. Three waves of large-scale migration of African Americans: first from the agricultural south to the industrialized northeast and midwest in the early 20th century, a second movement in the same direction with new additional destination to the West from roughly 1940 to 1970, and finally a reverse migration from other parts of the country to the urban south beginning in the late 20th century and continuing to the present. The depopulation of the rural Great Plains since the early 20th century, with many rural counties today having less than 40% of their 1900 population. A steady migration, starting during the Dust Bowl of the 1930s but accelerating after World War II, of all ethnicities toward the Sun Belt of the southern and western U.S. An ongoing migration of mostly working- and middle-class people of all ethnicities, but especially whites, from California to other states since about 1990, called the California Exodus. The United Kingdom has historically seen several migrations from the north of England to the south, and also from Scotland, Ireland (more recently Northern Ireland) and Wales to England. This was most prevalent during the industrial revolution, and also in the aftermath of the Great Famine of Ireland. In New Zealand, the drift to the north has seen the South Island gradually losing population to the main urban area, Auckland, in the country's far north. In Philippines, due to a centralised government and almost unequal distribution of government power and funds, people from the provinces head to Metro Manila to look for better jobs and opportunities. This has been continuing since then, although in much smaller numbers now, with Metro Cebu and Metro Davao now increasingly becoming