Triad societies originated in 17th century China when the Hung Mun came together in an attempt to overthrow the Qing dynasty in an unsuccessful bid to restore the Ming dynasty. Members were expected to regard each other as blood brothers, which is perhaps why they have become known colloquially as the Chinese mafia. There was a clear hierarchical structure within the group, initiation ceremonies and certain codes of conduct. In 19th century Hong Kong, members were frequently imprisoned under British law. Former Hong Kong triad member reflects on his life from gangster to rehabilitation worker By the 20th century, the Hung Mun had begun to break up into smaller gangs, based all over China. In 1949, the Chinese Communist Party came to power, prompting many gangs to flee to Hong Kong, as well as Macau,Taiwan and further overseas. Hong Kong soon became regarded as the triad capital, according to Chinese Triad Society by T. Wing Lo and Sharon Ingrid Kwok. In the 1960s, there were some 60 triad gangs in Hong Kong, with one in six people said to belong to one, according to police. Drug trafficking has traditionally been a significant source of income for gangs, with opium, heroin and cocaine all being traded. They also make money from fraud, extortion, money laundering, gambling and prostitution. They have often tried to extort money from local tradesmen or workers. Watch: Former Walled City heroin addict now helps teens quit drugs Violence between rival gangs is common. Prospective gang members are required to take the “36 oaths” as part of their initiation ceremony, in which they pledge to help free a fellow member if they inadvertently get him arrested. If they fail, they will be “killed by five thunderbolts”. Leading triad gangs in Hong Kong include the Sun Yee On, 14K and Wo Shing Wo. Between the 1950s and 1970s, the Kowloon Walled City, home to about 30,000 people, was largely controlled by the Sun Yee On and 14K. It fell into their hands soon after the end of the Japanese occupation in 1945, when refugees from the mainland found protection within its walls following China’s civil war. The British began to adopt a “hands-off” policy in relation to the walled city. It became a hotbed for crime. Residents also had to endure poor sanitation. The British and Chinese governments announced in January 1987 that the area would be demolished. Work began in 1993 and was completed the following year. The area has since been transformed into Kowloon Walled City Park. The Hong Kong police have a dedicated division that aims to combat triad activities – the Organised Crime and Triad Bureau. It is estimated there could be as many as 100,000 triad members currently operating in the city. When the Cross-Harbour Tunnel, which opened in 1972, was being built, fights reportedly broke out between rival gangs over who would control the bus drivers travelling through it. Despite various crackdowns, triad culture continues to be immortalised through films, artwork and video games.