<P> Following World War II, Pittsburgh launched a clean air and civic revitalization project known as the "Renaissance ." The industrial base continued to expand through the 1960s, but after 1970 foreign competition led to the collapse of the steel industry, with massive layoffs and mill closures . Top corporate headquarters moved out in the 1980s . In 2007 the city lost its status as a major transportation hub . The population of the Pittsburgh metropolitan area is holding steady at 2.4 million; 65% of its residents are of European descent and 35% are minorities . </P> <P> For thousands of years, Native Americans inhabited the region where the Allegheny and the Monongahela join to form the Ohio . Paleo - Indians conducted a hunter - gatherer lifestyle in the region perhaps as early as 19,000 years ago . Meadowcroft Rockshelter, an archaeological site west of Pittsburgh, provides evidence that these first Americans lived in the region from that date . During the Adena culture that followed, Mound Builders erected a large Indian Mound at the future site of McKees Rocks, about three miles (5 km) from the head of the Ohio . The Indian Mound, a burial site, was augmented in later years by members of the Hopewell culture . </P> <P> By 1700 the Iroquois Confederacy, the Five Nations - based south of the Great Lakes in present - day New York, held dominion over the upper Ohio valley, reserving it for hunting grounds . Other tribes included the Lenape (known by the English as Delaware), who had been displaced from eastern Pennsylvania by European settlement, and the Shawnee, who had migrated up from the south . With the arrival of European explorers, these tribes and others had been devastated by European infectious diseases, such as smallpox, measles, influenza, and malaria, to which they had no immunity . </P> <P> In 1748, when Conrad Weiser visited Logstown, 18 miles (29 km) downriver from Pittsburgh, he counted 789 warriors gathered: the Iroquois included 163 Seneca, 74 Mohawk, 35 Onondaga, 20 Cayuga, and 15 Oneida . Other tribes were 165 Lenape, 162 Shawnee, 100 Wyandot, 40 Tisagechroami, and 15 Mohican . </P>

Why did pittsburgh pennsylvania become the steel capital of the world