Urban decay (also known as urban rot and urban blight) is the process whereby a previously functioning city, or part of a city, falls into disrepair and decrepitude. It may feature deindustrialization, depopulation or changing population, economic restructuring, abandoned buildings, high local unemployment, fragmented families, political disenfranchisement, crime, and a desolate, inhospitable city landscape.
Since the 1970s and 1980s, urban decay has been associated with Western cities, especially in North America and parts of Europe. Since then, major structural changes in global economies, transportation, and government policy created the economic and then the social conditions resulting in urban decay.
The effects counter the development of most of Europe and North America; in countries beyond, urban decay is manifested in the peripheral slums at the outskirts of a metropolis, while the city center and the inner city retain high real estate values and sustain a steadily increasing populace. In contrast, North American and British cities often experience population flights to the suburbs and exurb commuter towns; that is, white flight. Another characteristic of urban decay is blight—the visual, psychological, and physical effects of living among empty lots, buildings and condemned houses. Such desolate properties are socially dangerous to the community because they attract criminals and street gangs, contributing to the volume of crime.
Urban decay has no single cause; it results from combinations of inter-related socio-economic conditions—including the city’s urban planning decisions, tight rent control, the poverty of the local populace, the construction of freeway roads and rail road lines that bypass the area, depopulation by suburbanization of peripheral lands, real estate neighborhood redlining, and immigration restrictions.
During the Industrial Revolution, from the late eighteenth century to the early nineteenth century, rural people moved from the country to the cities for employment in manufacturing industry, thus causing the urban population boom. However, subsequent economic change left many cities economically vulnerable. Studies such as the Urban Task Force (DETR 1999), the Urban White Paper (DETR 2000), and a study of Scottish cities (2003) posit that areas suffering industrial decline—high unemployment, poverty, and a decaying physical environment (sometimes including contaminated land and obsolete infrastructure)—prove "highly resistant to improvement".
Changes in means of transport, from the public to the private – specifically, the private motor car – eliminated some of the cities' public transport service advantages, e.g., fixed-route buses and trains. In particular, at the end of World War II, many political decisions favored suburban development and encouraged suburbanization, by drawing city taxes from the cities to build new infrastructure for remote, racially-restricted suburban towns.
The manufacturing sector has been a base for the prosperity of major cities. When the industries have relocated outside of cities, some have experienced population loss with associated urban decay, and even riots. Cut backs on police and fire services may result, while lobbying for government funded housing may increase. Increased city taxes encourage residents to move out.
United States 
Historically in the United States, the white middle class gradually left the cities for suburban areas because of higher crime rates and perceived danger caused by African-American migration north toward cities after World War I (the Great Migration)---the so-called "white flight" phenomenon.
Some historians differentiate between the first Great Migration (1910–1930), numbering about 1.6 million Black migrants who left mostly Southern rural areas to migrate to northern and midwestern industrial cities, and, after a lull during the Great Depression, a Second Great Migration (1940 to 1970), in which 5 million or more African-Americans moved, including many to California and various western cities.
Between 1910 and 1970, Blacks moved from 14 states of the South, especially Alabama, Louisiana, and Mississippi, to the other three cultural (and census-designated) regions of the United States. More townspeople with urban skills moved during the second migration. By the end of the Second Great Migration, African Americans had become an urbanized population. More than 80 percent lived in cities. A majority of 53 percent remained in the South, while 40 percent lived in the North and 7 percent in the West.
From the 1930s until 1977, Black Americans seeking borrowing capital for housing and businesses were discriminated against via the federal government legislated discriminatory lending practices for the Federal Housing Administration (FHA) via redlining. In 1977, the US Congress passed the Community Reinvestment Act, designed to encourage commercial banks and savings associations to help meet the needs of borrowers in all segments of their communities, including low- and moderate-income neighborhoods.
Later urban centers were drained further through the advent of mass car ownership, the marketing of suburbia as a location to move to, and the building of the Interstate Highway System. In North America this shift manifested itself in strip malls, suburban retail and employment centers, and very low-density housing estates. Large areas of many northern cities in the United States experienced population decreases and a degradation of urban areas.
Inner-city property values declined and economically disadvantaged populations moved in. In the U.S., the new inner-city poor were often African-Americans that migrated from the South in the 1920s and 1930s. As they moved into traditional white European-American neighborhoods, ethnic frictions served to accelerate flight to the suburbs.
United Kingdom 
Britain experienced severe urban decay in the 1970s and 1980s exemplified by the number 1 single in 1981, 'Ghost Town' by The Specials. The effect was often unknowingly assisted by public sector policies designed to clear 18th- and 19th-century slum areas and move people into state-subsidized, suburban housing.
Major cities like Glasgow, the towns of the South Wales valleys, and some of the major industrial cities like Birmingham, Manchester, Liverpool, Newcastle, and east London, all experienced population decreases, with large areas of 19th-century housing experiencing market price collapse.
Large French cities are often surrounded by areas of urban decay. Whilst city centers tend to be occupied mainly by upper-class residents, cities are often surrounded by public housing developments, with many tenants being French of North African origin (from former French colonies Morocco, Algeria and Tunisia), and recent immigrants.
From the 50s to the 70s, publicly funded housing projects resulted in large areas of mid to high-rise buildings. These modern "grand ensembles" were welcomed at the time, as they replaced shanty towns and raised living standards, but these areas were heavily affected by economic depression in the 80s.
The banlieues of large cities like Lyon and Marseilles, especially the Parisian banlieues (where there are 8 million residents), are severely criticized and forgotten by the country's territorial spacial planning administration. They have been ostracised ever since the French Commune government of 1871, considered as "lawless" or "outside the law", even "outside the Republic", as opposed to "deep France", or "authentic France", which is associated with the countryside.
In November 2005, the French suburbs were the scene of severe riots sparked by the accidental electrocution of two teenagers in the outskirts of Paris, and fueled in part by the substandard living conditions in these areas. Many deprived suburbs of French cities were suddenly the scenes of clashes between youngsters and the police, with violence and numerous car burnings resulting in huge media coverage.
Today the situation remains generally unchanged however, there is still a level of disparity. Some areas are experiencing increased drug trafficking, whilst some northern suburbs of Paris and areas like Vaulx-en-Velin are undergoing refurbishment and re-development.
Many mono-industrial cities in France know increasing criminality and decay; in the same time the population is going out. The issue remains a taboo in French public politics, because it shows that the French welfare state abandoned more than a half of the country, especially provincial mono-industrial isolated centers (10 to 50.000 inhabitants) as Pau, Vierzon, Fumel, Lucé,Roubaix and so on
Policy responses to urban decay 
The main responses to urban decay have been through positive public intervention and policy, through a plethora of initiatives, funding streams, and agencies, using the principles of New Urbanism (or through Urban Renaissance, its UK/European equivalent). Gentrification has also had a significant effect, and remains the primary means of a "natural" remedy.
United States 
In the United States, early government policies included "urban renewal" and building of large scale housing projects for the poor. Urban renewal demolished entire neighborhoods in many inner cities; in many ways, it was a cause of urban decay rather than a remedy. Housing projects became crime-infested mistakes. These government efforts are now thought by many to have been misguided.
For multiple reasons, some cities have rebounded from these policy mistakes. Meanwhile, some of the inner suburbs built in the 1950s and 60s are beginning the process of decay, as those who are living in the inner city are pushed out due to gentrification.
In Western Europe, where undeveloped land is scarce and urban areas are generally recognised as the drivers of the new information and service economies, urban regeneration has become an industry in itself, with hundreds of agencies and charities set up to tackle the issue. European cities have the benefit of historical organic development patterns already concurrent to the New Urbanist model, and although derelict, most cities have attractive historical quarters and buildings ripe for redevelopment.
In the inner-city estates and suburban cités, the solution is often more drastic, with 1960s and 70s state housing projects being totally demolished and rebuilt in a more traditional European urban style, with a mix of housing types, sizes, prices, and tenures, as well as a mix of other uses such as retail or commercial. One of the best examples of this is in Hulme, Manchester, which was cleared of 19th-century housing in the 1950s to make way for a large estate of high-rise flats. During the 1990s, it was cleared again to make way for new development built along new urbanist lines.
See also 
- Rural flight, the country counterpart
- Gentrification, the reverse process
- Modern ruins
- Ghost town
- Urban Sores: On the Interaction Between Segregation, Urban Decay, and Deprived Neighbourhoods, by Hans Skifter Andersen. ISBN 0-7546-3305-5. 2003.
- Crabgrass Frontier: The Suburbanization of the United States by Professor Kenneth T Jackson (1987)
- The Power Broker: Robert Moses and the Fall of New York, by Robert Caro, p.522.
The construction of the Gowanus Parkway, laying a concrete slab on top of lively, bustling Third Avenue, buried the avenue in shadow, and when the parkway was completed, the avenue was cast forever into darkness and gloom, and its bustle and life were forever gone.
- How East New York Became a Ghetto by Walter Thabit. ISBN 0-8147-8267-1. Page 42.
- Comeback Cities: A Blueprint for Urban Neighborhood Revival By Paul S. Grogan, Tony Proscio. ISBN 0-8133-3952-9. Published 2002. pp.139-145.
- Lupton, R. and Power, A. (2004) The Growth and Decline of Cities and Regions. CASE-Brookings Census Brief No.1
- Edward Glaeser, Andrei Schleifer, "The Curley Effect: The Economics of Shaping the Electorate", The Journal of Law, Economics, & Organization 21 (1): 12–13
- Boustan, L. P. (2010). "Was Postwar Suburbanization “White Flight”? Evidence from the Black Migration*". Quarterly Journal of Economics 125: 417–443. doi:10.1162/qjec.2010.125.1.417.
- William H. Frey, "The New Great Migration: Black Americans' Return to the South, 1965–2000", The Brookings Institution, May 2004, pp. 1–3, accessed 19 Mar 2008
- Principles to Guide Housing Policy at the Beginning of the Millennium, Michael Schill & Susan Wachter, Cityscape
- "Racial" Provisions of FHA Underwriting Manual, 1938[dead link]
Recommended restrictions should include provision for the following . . . Prohibition of the occupancy of properties except by the race for which they are intended . . . Schools should be appropriate to the needs of the new community and they should not be attended in large numbers by inharmonious racial groups. Federal Housing Administration, Underwriting Manual: Underwriting and Valuation Procedure Under Title II of the National Housing Act With Revisions to February, 1938 (Washington, D.C.), Part II, Section 9, Rating of Location.
- Text of Housing and Community Development Act of 1977 — Title VIII (Community Reinvestment)
- Avery, Robert B.; Raphael W. Bostic, Glenn B. Canner (November 2000). "The Performance and Profitability of CRA-Related Lending". Economic Commentary. Federal Reserve Bank of Cleveland. Retrieved 2008-10-05.
- "Community Reinvestment Act". Federal Reserve Board (FRB). Retrieved 2008-10-05.
- Urban Decline and the Future of American Cities By Katharine L. Bradbury, Kenneth A. Small, ., Anthony Downs Page 28. ISBN 0-8157-1053-4
Ninety-five percent of cities with populations greater than 100,000 people in the U.S. lost population between 1970 and 1975.
- White Flight: Atlanta and the Making of Modern Conservatism
- Anne-Marie Thiesse (1997) Ils apprenaient la France, l'exaltation des régions dans le discours patriotique, MSH.
- Encyclopedia of Chicago History
"(In Chicago) while whites were among those uprooted in Hyde Park and on the North and West Sides, urban renewal in this context too often meant, as contemporaries noted, "Negro removal". Between 1948 and 1963 alone, some 50,000 families (averaging 3.3 members) and 18,000 individuals were displaced."
- American Project: The Rise and Fall of a Modern Ghetto By Sudhir Alladi Venkatesh. ISBN 0-674-00830-8. 2002.
- The Decline of Inner Suburbs: The New Suburban Gothic in the United States By Thomas J. Vicino.
|Wikimedia Commons has media related to: Urban decay|
|Wikiquote has a collection of quotations related to: Urban decay|
- Images of the Chernobyl exclusion zone city of Pripyat
- Towards a Strong Urban Renaissance' Follow up report to UK Government's 'Urban task Force' report
- U.S based 'Urban Renaissance Institute'