At the same period, the feudalisation of the Kingdom of Sicily was intensified, through the enforcement of feudal bonds and relations among its subjects. The 1669 Etna eruption destroyed Catania. In 1693, 5% of the Kingdom's population was killed because of earthquakes. During that period, there were also plague outbreaks. The 17th and 18th century were an era of decline of the Kingdom. Corruption was prevalent among the upper and middle classes of the society. Widespread corruption and mistreatment of the lower classes by the feudal lords led to the creation of groups of brigands, attacking the nobility and destroying their fiefs. These groups, which were self-named "Mafia", were the foundation of the modern Sicilian Mafia. The escalation of revolts against the monarchy eventually led to the unification with Italy.