<Li> Mormon settlement of Utah </Li> <Li> California Gold Rush </Li> <Li> Klondike Gold Rush promoting settlement of Alaska </Li> <Li> Internal migration <Ul> <Li> African Americans escaped from slavery, sometimes via the Underground Railroad, reaching the free North before the American Civil War . </Li> <Li> In the 20th century, to seek jobs and escape racial violence, African Americans left the South in the Great Migration and Second Great Migration, moving to Northern, Midwestern, and Western cities, where they had to compete with recent European immigrants . </Li> <Li> Especially as transportation systems have improved over the centuries, it has become relatively easy for many Americans to move from one part of the country to another, given the lack of internal borders and dominance of English in most areas . Many do so for reasons of economic opportunity, climate, or culture . </Li> <Li> The American Industrial Revolution, promoted urbanization of what was previously a largely agrarian society </Li> <Li> Railroads, promoting migration westwards and streetcar suburbs, created significant ethnic shifts in urban areas . </Li> <Li> Economics and natural disasters have driven migration, for example during the Dust Bowl, World War II, and since the decline of the Rust Belt </Li> <Li> Suburbanization period after World War II, with "white flight" to new housing and away from later social unrest, followed by "black flight" </Li> <Li> The majority of Native Hawaiians who moved to the mainland U.S. have settled in California . </Li> <Li> Air conditioning has promoted migration from northern areas to the Sun Belt, aided by states' rules against union labor and having low taxes for businesses . The Jet Age promoted vacationing and part - time living in warmer areas (snowbirding). </Li> </Ul> </Li>

Which of the following is not a dominant social category in the united states