Mass migration refers to the migration of large groups of people from one geographical area to another. Mass migration is distinguished from individual or small scale migration; and also from seasonal migration, which may occur on a regular basis. A specific mass migration that is seen as especially influential to the course of history may be referred to as a 'great migration'. For example, great migrations include the Barbarian Invasions during the Roman Empire, the Great Migration from England of the 1630s, the California Gold Rush from 1848–1850, and the Great Migration of African Americans from the rural American south to the industrial north during 1920–1950.