irruption

noun

1. (countable, uncountable)The action of irrupting or breaking into; a violent entry or invasion; an inbreaking; an intrusion.

   “The Trojan irruption into the Greek camp is related in Book XV of the Iliad.”

   “[I]t was not till arts and ſciences began to revive after the irruption of the Barbarians into Europe, that any thing of this kind appeared.”

   “At that time it was thought that the critical section, in which an irruption of water from the river was to be feared, lay under the Shoots, but this proved not to be the case. Indeed, relatively little trouble was experienced from the Severn. The very serious flooding, which twice submerged part of the works, came from an underground river, (now known as the Great Spring), the presence of which was unsuspected.”

2. (countable, uncountable)An abrupt increase of an animal population.

   “Extreme rainfall events predict irruptions of rat plagues in central Australia.”

3. (broadly, countable, uncountable)An abrupt increase in the size of a movement or organization.

   “How can we explain this irruption of young people self-identifying as socialists?”