<P> Free market pressures exposed the U.S. steel industry's own internal problems, which included a now - outdated manufacturing base that had been over-expanded in the 1950s and 1960s, hostile management and labor relationships, the inflexibility of United Steelworkers regarding wage cuts and work - rule reforms, oligarchic management styles, and poor strategic planning by both unions and management . In particular, Pittsburgh faced its own challenges . Local coke and iron ore deposits were depleted, raising material costs . The large mills in the Pittsburgh region also faced competition from newer, more profitable "mini-mills" and non-union mills with lower labor costs . </P> <P> Beginning in the late 1970s and early 1980s, the steel industry in Pittsburgh began to implode along with the deindustrialization of the U.S. Following the 1981--1982 recession, for example, the mills laid off 153,000 workers . The steel mills began to shut down . These closures caused a ripple effect, as railroads, mines, and other factories across the region lost business and closed . The local economy suffered a depression, marked by high unemployment and underemployment, as laid - off workers took lower - paying, non-union jobs . Pittsburgh suffered as elsewhere in the Rust Belt with a declining population, and like many other U.S. cities, it also saw white flight to the suburbs . </P> <P> In 1991 the Homestead Works was demolished, replaced in 1999 by The Waterfront shopping mall . As a direct result of the loss of mill employment, the number of people living in Homestead dwindled . By the time of the 2000 census, the borough population was 3,569 . The borough began financially recovering in 2002, with the enlarging retail tax base . </P> <P> Top corporate headquarters such as Gulf Oil (1985), Koppers (1987), Westinghouse (1996) and Rockwell International (1989) were bought out by larger firms, with the loss of high paying, white collar headquarters and research personnel (the "brain drain") as well as massive charitable contributions by the "home based" companies to local cultural and educational institutions . At the time of the Gulf Oil merger in 1985 it was the largest buyout in world history involving the company that was No. 7 on the Fortune 500 just six years earlier . Over 1,000 high paying white collar corporate and PhD research jobs were lost in one day . </P>

What was the main reason pittsburgh became an industrial center during the late 1800's