During its long history, small country of Singapore tried for centuries to win its independence from the hands of various empires (China, Sultanate of Johor and others). As a British Colony, they survived Japanese World War 2 occupation (1942-1945) and finally declared independence on 31 August 1963 as a part of Malaysia (two years later, they also separated from them). In the following years,Singapore established its powerful manufacturing industry, which together with great sea trade routes position brought immense wealth to the entire country.
This sudden economic boom also brought rise to the widespread vandalism in the younger parts of their population. Public city workers during early 1980s had great trouble cleaning the city streets, staircases, elevators, pavements, city busses and other public areas from never-ending chewing gum waste. First official mentioning of this problem came in 1983 when Prime MinisterLee Kuan Yew received first draft of the proposal that wanted to ban use of chewing gum, but it was not passed. In 1987, Singapore unveiled their brand new $5 billion metro system, but unfortunately, it soon became the target of the never-ending vandalism attacks. Chewing gums were constantly left on the top of the seats, hand holders and even automatic door sensors (witch brought great financial problems to the metro maintenance staff).
Official chewing gum ban became active in 1992 with the acceptance of the Control of Manufacture Act (Singapore Statute Chapter 57) that restricted the use, distribution and trade of all kinds of chewing gums. Police started enforcing strict measurements for punishment of anyone who disturbed the public areas with chewing gum leftovers and spitting. Import of all kinds of chewing gums ceased immediately, but minor window remained in place for local stores to sell their dwindling stock. In 2004, international pressure from United States brought the change in the Singaporean law that reinstated the legal use of some small amounts of therapeutic dental chewing gums. Their use is heavily regulated and has to be purchased directly from dentist or doctor (if they fail to send your credentials to the government, then they can be jailed up to two years and fined $3,000).
Tourists that visit Singapore are allowed to bring chewing gum with them, but only maximum of two packs per person. Any more than that and they will be susceptible to be charged with "gum smuggling" which carries the penalty of one year in jail and $5,500 fine. People that are caught with leaving chewing gum remains in the public space can be charged with monetary fine, community work, or often - public beating with the bamboo stick.
Black market for "chewing gums" does not exist in the Singapore, and majority of population that want to enjoy them often go to neighboring countries where they are legal. To this day, Singaporean 16 year old kids can more easily visit prostitutes (which is legal in some parts of the country) than gain possession of a chewing gum.