The lore of Saṃsāra only goes back nine thousand years. In that time there have been a few major and lots of minor wars. Most of the wars have been navel battles between island countries.
There are also scars that have been left on the land and water by magic. Some of these are now only visual records of what happened while others still have active magic.
Each scar that is left behind has a story for why it is there.