Formerly, a street or quarter of a city set apart as a legally enforced residential area for Jews. Forced segregation of Jews spread throughout Europe in the 14th–15th centuries. Ghettos were customarily enclosed with walls and gates and kept locked at night and during Christian festivals. Since outward expansion was usually impossible, most ghettos grew upward; congestion, fire hazards, and unsanitary conditions often resulted. Ghettos were abolished in western Europe in the 19th century; those revived by the Nazi Party (seeWarsaw Ghetto Uprising) were overcrowded holding places preliminary to extermination. More recently, the term ghetto has been applied to impoverished urban areas exclusively settled by a minority group or groups and perpetuated by economic and social pressures rather than legal and physical measures.