American cities often declare blighted status once determined that urban renewal strategies are the most appropriate means to encourage the private investment for reversing deteriorating downtown conditions. Historically in the United States, the white middle class gradually left the cities for suburban areas due to African-American migration north toward cities after World War I. Countries United States ДЇurther information: Rust Belt and United States cities by crime rate Libertarian economists argue that rent control contributes to urban blight by reducing new construction and investment in housing and deincentivizing maintenance. Increased city taxes encourage residents to move out.

Cut backs on police and fire services may result, while lobbying for government funded housing may increase. When the industries have relocated outside of cities, some have experienced population loss with associated urban decay, and even riots. The manufacturing sector has been a base for the prosperity of major cities. 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 towns. Д¬hanges 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. 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'. However, subsequent economic change left many cities economically vulnerable. Дuring the Industrial Revolution, from the late 18th century to the early 19th century, rural people moved from the country to the cities for employment in manufacturing industry, thus causing the urban population boom. 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-or run through-the area, depopulation by suburbanization of peripheral lands, real estate neighborhood redlining, and immigration restrictions. Another characteristic of urban decay is blight-the visual, psychological, and physical effects of living among empty lots, buildings and condemned houses. In contrast, North American and British cities often experience population flights to the suburbs and exurb commuter towns often in the form of white flight.

The effects counter the development of most of Europe and North America on other continents, 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. Since then, major structural changes in global economies, transportation, and government policy created the economic and then the social conditions resulting in urban decay. Since the 1970s and 1980s, urban decay has been associated with Western cities, especially in North America and parts of Europe (mostly the United Kingdom and France). It may feature deindustrialization, depopulation or deurbanization, economic restructuring, abandoned buildings or infrastructure, high local unemployment, increased poverty, fragmented families, low overall living standards or quality of life, political disenfranchisement, crime, elevated levels of pollution, and a desolate cityscape known as greyfield or urban prairie.

Urban decay (also known as urban rot, urban death and urban blight) is the sociological process by which a previously functioning city, or part of a city, falls into disrepair and decrepitude. Michenzani housing project, Ng'ambo, Zanzibar City, Tanzania