I've only played for about a year, but I've had varying luck.
Sometimes, I get three raids in a row, and then nothing for days and days. So I guess it's really just luck.
Ooops.
I hope you handled the trolls well.
I generally just pull the mobs away from my base and walk for the 90 seconds the event lasts, and kill them only after that - otherwise, new ones will respawn.
Which is great in the Wolf event, but otherwise a pain.
@Fratm The default setting is a 20% chance every 46 minutes.

Randomly happening events cause lots of enemies to spawn around the players. Progressing in the game world by defeating bosses causes harder events to appear. Events can be world-based or player-based depending on the world modifier settings in use. World-based events are the default mode. For most events to end, a player must stay in the active event area until the timer runs out. The event timer is paused if there are no players in the event area (except for the "You are being hunted...