Explanation: The Roman Emperor Septimius Severus, a mixed-race man from North Africa, was known for his... soldierly way of dealing with problems. That is to say, violence was always an option. While also renowned for his cunning, his lack of love for luxury, and his cultured outlook, Severus always seemed to be fond of returning to the "I have the sword and you don't" method of rulership.
Notably, near the end of his life, he embarked on a hybrid exploration-conquest of Caledonia - roughly modern-day Scotland. Supposedly, he reached the northern edge of Britannia and took astronomical measurements. As had happened several times before, the Caledonians met the Romans in battle essentially once, and then decided to hell with it - and scattered into the rough terrain of Scotland. Rather than a Roman victory, this was the start of guerilla warfare, wherein Roman scouting and foraging parties would be ambushed when detached from the Roman army and (ideally) eliminated.
This method of warfare so infuriated Severus that he swore to exterminate the Caledonians, down to the last man, woman, and child.
His two sons, in perhaps the only wise move either of them ever made in their lives, decided not to waste their time attempting to genocide Scotland, and abandoned the campaign immediately after Severus passed away from illness.