Final answer:
Pittsburgh evolved from a defensible site to an urban metroplex due to industrial growth spurred by the steel industry, changes in transportation and production methods with the advent of the steam engine, and socio-economic dynamics including 'white flight' and suburbanization.
Step-by-step explanation:
Pittsburgh's transformation from a defensible site to an urban metroplex is tied to the evolution of American cities and their changing roles in response to industrial and economic developments. Initially, cities like Pittsburgh were compact and served defensive purposes due to their strategic locations. For instance, Pittsburgh is located at a confluence site where the Allegheny and Monongahela rivers merge to form the Ohio River, providing a natural defense advantage and creating opportunities for river-borne trade.
However, with the Industrial Revolution and the advent of the steam engine, the need for cities to be limited by natural power sources such as rivers declined. Factories could be built near urban centers like Pittsburgh, which led to rapid urban growth. The city's industry, particularly steel production, thrived due to the availability of iron and coal in the region. This growth attracted a large workforce and required a city infrastructure that supported a much larger population, leading to urban expansion.
The concept of 'white flight' and suburbanization also contributed to changing the dynamics of Pittsburgh and similar cities. As minority populations and the impoverished migrated to cities for opportunities, white and middle-class residents often moved to the suburbs, taking with them substantial amounts of tax revenue. This exacerbated the financial strain on urban areas and shifted wealth to the suburbs, creating a stark contrast between the city and suburban environments.