Based in Italy and the U.S., the Mafia is a network of organized-crime groups active in a range of underworld ventures, from drug trafficking to murder. The Mafia evolved over centuries in Sicily, an island off the southern tip of Italy that until 1861 was ruled by a line of foreign invaders. Sicilians banded into groups to protect themselves; by the 19th century, some of these groups emerged as private armies that extorted protection money from landowners and evolved into the criminal enterprise known today as the Sicilian Mafia. The American Mafia, a separate entity, rose to power in the Prohibition era of the 1920s and soon flourished. By the late 20th century, however, anti-racketeering laws and other techniques brought down high-ranking mobsters both in Italy and the United States. By the early 21st century, the Mafia had been weakened but it still has not been driven out of business.