The Great Swarming is the event where the Kitin were first encountered and then set out to destroy Hominity.
“In their interminable quest for the dragon, in 2481 Fyros miners uncovered a nest of kitins in the Prime roots. Fraught with fear and horror, their first reflex was to destroy the first giant insects they came across. But alerted by the slaughter, legions of soldiers kitins suddenly surged forth from underground galleries to eradicate what they considered as their natural enemy. Homin cities were decimated, entire populations perished, and the great civilizations crumbled in a matter of days.[1]
Official website