Nobody has any real idea of how the different species interacted. In some cases there was probably peaceful interaction, it's why a lot of people have traces of Neanderthal blood.Not really. I live in a country that had the better part of 500 years with no major conflicts - Japan. The Edo period is pretty marked by the fact that while it started pretty bloody and ended horrifically, the centuries in between were largely peaceful. The Korean penninsula is largely the same. Centuries of peace.
There are lots and lots of examples throughout history of peace. The notion of "constant warfare" is not a reasonable reading of history. And, let's not forget, that prior to the 20th century, and certainly prior to the Renaissance, wars were very, very small things by and large and largely left the non-combatants out of it.
All we really know is that we're still here and none[/] of them are around any more. Odds are, over the long run we decided killing them off was just survival of the fittest.
As far as how what did or did not happen in the real world relates to games, I see no correlation at all. Every DM and group should decide what makes sense to them.