Anarchism is a political philosophy that advocates stateless societies often defined as self-governed voluntary institutions, but that several authors have defined as more specific institutions based on non-hierarchical free associations. Anarchism holds the state to be undesirable, unnecessary, or harmful. While anti-statism is central, some argue that anarchism entails opposing authority or hierarchical organisation in the conduct of human relations, including, but not limited to, the state system.
The central tendency of anarchism as a social movement has been represented by anarcho-communism and anarcho-syndicalism, with individualist anarchism being primarily a literary phenomenon which nevertheless did have an impact on the bigger currents and individualists have also participated in large anarchist organisations. Many anarchists oppose all forms of aggression, supporting self-defense or non-violence (anarcho-pacifism), while others have supported the use of some coercive measures, including violent revolution and propaganda of the deed, on the path to an anarchist society.
Since the last third of the 20th century, anarchists have been involved in student protest movements, peace movements, squatter movements, and the anti-globalization movement, among others. Anarchists have participated in violent revolutions (such as in Revolutionary Catalonia and the Free Territory) and anarchist political organizations (such as IWA-AIT or the IWW) exist since the 19th century.
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