It is an extreme form of urban autonomy, which can be expressed in less formal terms or by ordinary legislation such as a city charter.
In medieval times such measures as the Magdeburg rights established special status for cities and their residents in commercial relations.
Modern theorists of local civic economies, including Robert J. Oakerson and Jane Jacobs, argue that cities reflect a clash of values, especially of tolerances versus preferences, with views of the city varying from a pure community to that of a pure marketplace.
By contrast, those who choose downtown living tend to see it as more of a community, but must pay careful attention to their tolerances (for smog, noise pollution, crime, taxation, etc.).
Secession (the setup of entirely new legislative and executive entities) is advocated by certain urban theorists, notably Jane Jacobs, as the only way to deal politically with these vast differences in culture between modern cities and even their nearest suburbs and essential watersheds.
"[citation needed] She rejected the lesser "Charter" and less formal solutions, arguing the full structure of real regional government were necessary, and applied to the urban area alone.
Jacobs likewise took part in blocking the development of the Lower Manhattan Expressway in the 1960s, opposing Robert Moses.
A modern instance of a city-state is the Republic of Singapore, which was expelled from Malaysia for a variety of political and social reasons.
The other two existing and de jure city-states are Monaco and Vatican City, which operate as, nominally, politically independent urban areas.
Specifically, the status of a special administrative regions (SAR) has been conferred upon Hong Kong and Macau in the People's Republic of China.
The reason for their relative autonomy stems from their existence for more than a century as European colonies, and a resultant difficulty of full reintegration.
In South Korea, the main criterion for granting secession from the province is a population reaching one million.
In Indonesia, the capital Jakarta was once part of West Java until it gained special autonomy status and broke away from its former province in 1961.
For many decades, the urban communities of Toronto, Montreal and Vancouver have been configured separately from their respective provinces, for purposes of apportioning Members of Parliament after the national censuses conducted every five years.
Whether the new county-equivalent jurisdiction is considered to be a consolidated city-county like Philadelphia, Pennsylvania or San Francisco, California or an independent city like St. Louis, Missouri is a matter for each such state to decide.