"History is writen by the victor" is more than a cliché. Rulers have been editing history to make their actions seem justified for a long time. It might be the end of that era though, the internet is really changing the way our collective memory is working.

There's a theory out there that says a chunk of the middle ages never happened, and it's surprisingly plausable as conspiracy theories go. I don't really remember specifics, but it's worth a read if you stumble across the topic.