Pittsburgh, known as the "Steel City," was a major hub for the steel industry in the late 19th and early 20th centuries. The city's location along the Ohio River and its access to coal and iron ore made it an ideal site for steel production. Companies like Carnegie Steel played a significant role in the industrial boom, contributing to the city's rapid growth and economic development. As the demand for steel increased, Pittsburgh became a center for manufacturing and innovation. The city's factories and mills attracted a diverse workforce, including many immigrants seeking better opportunities. However, by the late 20th century, the decline of the steel industry led to economic challenges, prompting Pittsburgh to diversify its economy.