The thing is that pretty much everyone was raiding during the game timeframe and the biggest and most effective raiders was not people like the Scandinavians but what you call for more civilized nations like the Byzantine Empire.
So why is raiding such a limited mechanic compared to its widespread reality and why can't some if not the best raiders of the time period actually even raid?
So why is raiding such a limited mechanic compared to its widespread reality and why can't some if not the best raiders of the time period actually even raid?