Slum clearance in the United States has been used as an urban renewal strategy to regenerate derelict or run-down districts, often to be replaced with alternative developments or new housing. Early calls were made during the 19th century, although mass slum clearance did not occur until after World War II with the introduction of the Housing Act of 1949 which offered federal subsidies towards redevelopments. The scheme ended in 1974 having driven over 2,000 projects with costs in excess of $50 billion.