Although the crime threat in Bangkok is relatively low, non-confrontational crimes of opportunity such as pick-pocketing, purse-snatching, and credit card fraud occur with frequency. Bangkok's growth since the 1960s has been followed by increasing crime rates partly driven by urbanisation, migration, unemployment and poverty. By the late 1980s, Bangkok's crime rates were about four times that of the rest of the country. The police have long been preoccupied with street crimes ranging from housebreaking to assault and murder. The 1990s saw the emergence of vehicle theft and organized crime, particularly by foreign gangs. Drug trafficking, especially that of ''ya ba'' methamphetamine pills, is also chronic.