irruption

Etymology

From Middle French irruption, from Latin irruptio.

noun

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.
   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. 1948 September and October, “Weekend Works in the Severn Tunnel”, in Railway Magazine, page 299
2. (ecology) An abrupt increase of an animal population.
   Extreme rainfall events predict irruptions of rat plagues in central Australia.
3. (by extension) An abrupt increase in the size of a movement or organization.
   How can we explain this irruption of young people self-identifying as socialists?