人口不足
Population trends Population decline from 1950 to 1990 was due to a string of industrial plant closures. Plants such as Pittsburgh Plate Glass, Allegany Munitions and Celanese closed down and relocated as part of widespread industrial restructuring after WWII. The 1987 closure of the Kelly Springfield Tire Plant marked a turning point, as it was the last major manufacturing plant in the city limits to close its doors.