I was playing peaceful vikings, when all the sudden some raging mad viking declared a formal war on me (myself). Then the Sumerians, of which we had a friendship formally declared, declared a formal war upon me. This is also 410 BC. Running version 18.104.22.168 I have a save file, attached. Just click "next turn". Accept or decline the trade deals; it makes no difference. Only thing of noteworthiness that might have happened previous turn was I had found the dead sea within Sumerian lands.