Irruption

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."

2. An abrupt increase of an animal population.

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

3. An abrupt increase in the size of a movement or organization.

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