On 1 May every year trade unions, left-wing organisations and social activists march in rallies to mark International Workers' Day: the day when workers across the world were granted rights that many take for granted today. This year many of the demonstrations were marked by violence, as people expressed their anger at police violence and unregulated capitalism.

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A Salvadoran worker shouts slogans as he takes part in a demonstration along a main avenue of San Salvador during May Day celebrations.Marvin Recinos/AFP/Getty Images
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A demonstrator gestures against policemen during a demonstration during May Day celebrations in Medellin, Antioquia department, Colombia.Raul Arboleda/AFP/Getty Images
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Demonstrators show their support for the campaign against racism and police violence in the US during a May Day protest in Oakland, California.Josh Edelson/AFP/Getty Images
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Demonstrators show their support during a May Day protest in Oakland, California. Josh Edelson/AFP/Getty Images
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A demonstrator jumps on a car at a dealership during a May Day protest in Oakland, California on 1 May 2015.Josh Edelson/AFP/Getty Images
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A crowd of demonstrators march up a hill during a May Day protest in Oakland, California. Josh Edelson/AFP/Getty Images
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Protesters chant during a May Day rally in downtown Los Angeles, California. Many of the protesters were calling on leaders in Washington to come up with a comprehensive immigration plan, higher wages for minimum wage earners.Photo by Sandy Huffaker/Getty Images
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Protesters chant during a May Day rally in downtown Los Angeles, California. Protestors in LA also spoke out against police brutality.Photo by Sandy Huffaker/Getty Images
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A man walks past soldiers from the National Guard in the Western District in Baltimore, Maryland on 1 May 2015. Many May Day rallies held in the US also expressed support for the Black Lives Matter campaign and anger at high levels of violence used by US police.Andrew Caballero-Reynolds/AFP/Getty Images
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Demonstrators participate in a May Day march in Chicago, Illinois. The demonstration was one of many around the world on what has become known as International Workers Day.Photo by Scott Olson/Getty Images
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Demonstrators take part in a May Day demonstration in Bogota, Colombia.Guillermo Legaria/AFP/Getty Images
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Riot policemen arrive at the Bolivar's square to control a May Day demonstration in Bogota, Colombia.Guillermo Legaria/AFP/Getty Images
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A elderly demonstrator takes part in a May Day demonstration in Bogota, Colombia.Guillermo Legaria/AFP/Getty Images
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Sightseers follow the participants in a 'Revolutionary May 1st' May Day march in Berlin, Germany. Anti-capitalist demonstrations on May Day are an annual tradition in Berlin, and the protests often turn violent with clashes between marchers and riot police.Carsten Koall/Getty Images
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Participants wear masks in a 'Revolutionary May 1st' May Day march in Berlin, Germany. Approximately 30,000 demonstrators were expected to participate in the march.Carsten Koall/Getty Images
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A wounded demonstrator is escorted by riot policemen during a rally to celebrate May Day in Bogota, Colombia.Guillermo Legaria/AFP/Getty Images
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A demonstrator confronts riot policemen during a demonstration to celebrate May Day in Bogota, Colombia.Guillermo Legaria/AFP/Getty Images