Pittsburgh

===20th century===
[[File:Thaddeus M. Fowler - Pittsburgh, Pennsylvania 1902.jpg|thumb|alt=Bird's Eye View of Pittsburgh, 1902|An aerial view of Pittsburgh in 1902<ref>{{cite web |url=https://tedsvintageart.com/products/pittsburgh-pennsylvania-1902-historical-map/ |title=Vintage Map of Pittsburgh, Pennsylvania 1902 - Ted's Vintage Art |website=Teds Vintage Art - Buy Historic Art Prints & Wall Decor|access-date=June 3, 2019}}</ref>]]
[[File:Mills in Strip District, Pittsburgh (84.41.70).jpg|thumb|Steel mills in the [[Strip District, Pittsburgh|Strip District]] in 1906]]
In 1901, [[J. P. Morgan]] and attorney [[Elbert Henry Gary|Elbert H. Gary]] merged [[Carnegie Steel Company]] and several other companies into [[U.S. Steel]]. By 1910, Pittsburgh was the [[Largest cities in the United States by population by decade|nation's eighth-largest city]], accounting for between one-third and one-half of national steel output.

The [[Pittsburgh Agreement]] was subscribed in May 1918 between the Czech and Slovak nationalities, as envisioned by [[T. G. Masaryk]], concerning the future foundation of [[Czechoslovakia]].<ref>PRECLÍK, Vratislav. Masaryk a legie (Masaryk and legions), váz. kniha, 219 str., vydalo nakladatelství Paris Karviná, Žižkova 2379 (734 01 Karviná) ve spolupráci s Masarykovým demokratickým hnutím (Masaryk democratic movement, Prague), 2019, {{ISBN|978-80-87173-47-3}}, s. 8 - 48, s. 84 - 124, s. 125 - 148, s. 157, s. 164 - 169, s. 170 - 194</ref>

The city suffered severe flooding in March 1936.

The city's population swelled to more than a half million, attracting numerous European immigrants to its industrial jobs. By 1940, non-Hispanic whites were 90.6% of the city's population.<ref>{{cite web |title=Race and Hispanic Origin for Selected Cities and Other Places: Earliest Census to 1990 |publisher=U.S. Census Bureau |url=https://www.census.gov/population/www/documentation/twps0076/twps0076.html |access-date=January 3, 2012 |url-status=dead |archive-url=https://web.archive.org/web/20120812191959/http://www.census.gov/population/www/documentation/twps0076/twps0076.html |archive-date=August 12, 2012}}</ref> Pittsburgh also became a main destination of the African-American [[Great Migration (African American)|Great Migration]] from the rural South during the first half of the 20th century.<ref>{{cite web |url=http://old.post-gazette.com/lifestyle/20030218kids0218p9.asp |title=Kids' Corner: 1910-30 saw huge black migration |last=Boucher |first=Amber |date=February 18, 2003 |website=[[Pittsburgh Post-Gazette]] |access-date=May 18, 2019 |archive-date=December 9, 2018 |archive-url=https://web.archive.org/web/20181209121819/http://old.post-gazette.com/lifestyle/20030218kids0218p9.asp |url-status=dead }}</ref> Limited initially by discrimination, some 95% percent of the men became unskilled steel workers.<ref>Lubove, Roy, ed. ''Pittsburgh.'' New York: New Viewpoints, 1976.</ref>

During [[World War II]], demand for steel increased and area mills operated 24 hours a day to produce 95&nbsp;million tons of steel for the war effort.<ref name="Lorant"/> This resulted in the highest levels of air pollution in the city's almost century of industry. The city's reputation as the "arsenal of democracy"<ref>{{cite web |url=https://news.google.com/newspapers?id=_ssaAAAAIBAJ&pg=3214%2C363940 |title=The Pittsburgh Press – Google News Archive Search|access-date=June 11, 2015}}</ref><ref>{{cite web |url=http://www.pittsburghmagazine.com/Pittsburgh-Magazine/December-2013/The-Way-We-Were/ |title=The Way We Were |date=November 21, 2013|access-date=June 11, 2015}}</ref> was being overshadowed by [[James Parton]]'s 1868 observation of Pittsburgh being "hell with the lid off."<ref>{{cite news |last=Kalson |first=Sally |title=Cartoonist draws, fires a blank with Pittsburgh joke |work=Pittsburgh Post-Gazette |date=November 19, 2003 |url=http://www.post-gazette.com/columnists/20031119sally104col2p2.asp}}</ref>

Following World War II, the city launched a clean air and civic revitalization project known as the "Renaissance," cleaning up the air and the rivers. The "Renaissance II" project followed in 1977, focused on cultural and neighborhood development. The industrial base continued to expand through the 1970s, but beginning in the early 1980s both the area's steel and electronics industries imploded during national industrial restructuring. There were massive layoffs from mill and plant closures.<ref name="diaspora"/>

In the later 20th century, the area shifted its economic base to education, tourism, and services, largely based on healthcare/medicine, finance, and high technology such as robotics. Although Pittsburgh successfully shifted its economy and remained viable, the city's population has never rebounded to its industrial-era highs. While 680,000 people lived in the city proper in 1950, a combination of suburbanization and economic turbulence resulted in a decrease in city population, even as the metropolitan area population increased again.