sentences:  Accepting the premise of shrinking cities as result of economic decline and urban out-migration, Friedrichs discusses how and why this initial economic decline occurs.Through a dissection of the theory of product life-cycle and its suggestion of urban decline from disinvestment of outdated industry, Friedrichs attributes the root cause of shrinking cities as the lack of industrial diversification within specific urban areas.This lack of diversification, Friedrichs suggests, magnifies the political and economic power of the few major companies and weakens the workers' ability to insulate against disinvestment and subsequent deindustrialization of cities.