In the far eastern side of The Cursed Forest, you will come to a Remote Hunting Lodge. Inside is Old Mage. Talk to him and he will offer to show you the origin of The Cursed Forest battle.
You agree and he teleports you back in time. You walk a short distance and find the happy couple having a picnic.
You start talking to them and things start to turn sour, real fast.
Having seen all there is to see, you are automatically teleported back to the Remote Hunting Lodge. This quest is complete, but you have to wonder if your presence was the catalyst that sparked the war.