Just After you kill moder , activates fuling horde raid , so its just that
Horde go off when you kill last boss but will activate night fuling patrols everywhere
Try to make a moat to save your outspots , your girlfriend can be a good archer if know how position over a stone wall

Every time you kill a boss, it unlocks the base attacks/Raids for the next boss. Basically whoever your next boss fight is will send enemies to attack your base, until you kill the boss of that biome.

When you first start the game and haven't killed any bosses, Eikthyr will raid:
"Eikthyr rallies the creatures of the forest"

When you kill Eikthyr, The Elder will start sending raids:
"The forest is moving..."

When you kill The Elder, Bonemass will start sending raids:
"A foul smell from the swamp"

When you kill Bonemass, Moder will start sending raids:
"A cold wind blows from the mountains"

When you kill Moder, Yagluth will start sending raids:
"The horde is attacking"

Each of these raids are affected by enemies you kill as well, sometimes adding them to the raids (like Blobs to the Foul Smell From The Swamp raid) and also killing bosses will permanently add raids as well, such as "The ground is shaking" Troll Attack which happens after you kill The Elder, and have killed a Troll.

there is a command to reset the events if you wished it so - think to reactivate you just kill boss again, not sure....look through all the commands list

I haven't killed Bonemass yet but have been raided by the swamp. I think it's more about discovering the summoning area.

Originally posted by ShaftAlmighty:

I haven't killed Bonemass yet but have been raided by the swamp. I think it's more about discovering the summoning area.

Read above , you will get raided by the swamp when u kill the elder , not after bonemass , in that case you will get raided by drakes/wolves