There are many economic, social and physical reasons why people emigrate and they can usually be classified into push and pull factors.
What are push and pull factors?
Economic motives loom large in all human movements, but are particularly important with regards to migration.
Sometimes this is encouraged by the destination country for example, the 1960’s employment campaign in the Caribbean by London bus companies that actively recruited young men to move to London to work as bus drivers, who were then often followed by their families.
Another example might be the “brain drain” to America that occurred in the latter half of the 20th century from several other western countries.
Economic push factors tend to be the exact reversal of the pull factors:
This lack of economic opportunity tends to push people to look for their futures outside the area of their origin.
An example of this is the migration of Mexicans and people from other Central American countries into the US, where they often work low-wage, long-hour jobs in farming, construction and domestic labour.
It’s difficult to classify this case purely with push factors though, because often the factors associated with the country of origin are just as important as the factors associated with the country of destination.
Forced migration has also been used for economic gain, such as the 20 million men, women and children who were forcibly carried as slaves to the Americas between the 16th and 18th centuries.
Social reasons tend to involve forced migration
For example the US attracted religious refugees, such as the Mennonites, who settled in Pennsylvania.
Examples being the Huguenots in 16th century France, the Puritans in 17th century England and the Jewish refugees from Nazi Germany.
For example the Alps pull French people to eastern France. Spain attracts migrants, especially retirees, who seek warmer winters
Examples would be the east African drought of 2011 and the mass exodus from the island of Montserrat leading up to the eruption of the *La Soufriere Hills volcano in 1995, which led to two thirds of the population abandoning the island.
*(Don’t confuse with La Soufriere on the island of Saint Vincent, or La Grande Soufriere on the island of Basse-Terre.)