Title: What is a historical bias? - Quora
Headings: 
What is a historical bias?
Content: History is written by whoever has a method of recording events. The secluded monasteries that the Danes sacked and looted during the Viking Age were the “losers”, and yet they were the ones who recorded early Viking raids on England. The Mongols defeated several of the Rus’ princes at the Battle of the Kalka River in 1223 and later subjugated many of the Rus’ principalities, and yet much of the information we have on the Mongol Invasion of Eastern Europe comes from Rus’ chroniclers. You’ll probably notice that the “victors” in those two examples are traditionally portrayed as murderous barbarians. That’s partially because much of the accounts of those events often come from the “losers”. If the “loser” has a more effective method of recording events, then we’re more likely to hear the loser’s side of the story. That’s why the Vikings are traditionally described as bloodthirsty heathens: they raided the exact people who typically recorded historical events.* When you think of the “victors” throughout history who are traditionally portrayed as savages or barbarians, there’s a chance that the people they defeated had a writing system while the “victor” did not. With that—and, well, a whole host of other factors—in consideration, the notion that history is written by the victors simply isn’t true.