Of course they're raiding, it's just their way. But once you play as the Greenskins their strange behaviour starts to make sense and you'll oddly find yourself sympathising with them. Then, when you finally turn to attack them, they roll up with a Waaagh! that has Grimgor Ironhide at its head and he's somehow three levels higher than your own best legendary lord. When you encounter the Greenskins while playing as other factions they're a constant annoyance, showing up when you're busy at war with someone else to raid your lands and drain your bank account and public order.
