What is neat is that after the people in those oppressive regimes faking the news die the archeological evidence they leave behind paints a much clearer image. Even more recent stuff like the move of the Benin Bronzes into the British Museum in 1897, after they were forcibly taken from Nigerian natives in the Kingdom of Benin when a British Diplomat thought it apt to kill the king and loot the palace instead. They were, for decades, known as upright officials, but now the entire world has a very complete timeline of every single action they took on their atrocity filled adventure.

Even things as far back as the western history of Greece and Egypt that people are so accustomed to has been thoroughly examined and refuted by archaeological evidence.

The only cases where this isn't true, yet, is when literally nothing was left behind by the invaders: like with the Catholic Crusades against the Vikings in the 12th and 13th century, destroying some of their languages and cultures completely. Someday, though, we might know more about what they believed in or how to read their runes instead of taking the Church's word for it.