irruption

Noun

irruption (countable and uncountable, plural irruptions)

1. 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.1748, [Tobias Smollett], The Adventures of Roderick Random. […] In Two Volumes., 2nd edition, volume I, London: Printed for J. Osborn in Pater-noster-Row, →OCLC, page vi
2. An abrupt increase of an animal population.
   • Extreme rainfall events predict irruptions of rat plagues in central Australia.
3. (broadly) An abrupt increase in the size of a movement or organization.
   • How can we explain this irruption of young people self-identifying as socialists?