I got a quest that wanted me to search some ruins while avoiding roaming armies defending it. After searching the correct ruin I thought that the roaming armies would de-spawn. Instead I get this:

I apologize for the picture's quality, but it should be clear enough that the 5 armies that the quest spawned are now beseiging my city. I know that I'm not very good at this game, but having to fight off 28 units besieging my city at turn 70 seems a little impossible. I've seen them embark too, assuming that they'll continue to attack me this means my game is over. Has anyone else encountered this?

I know that one of the quests introduced in the latest DLC can be triggered too early and is similarly game-ending, but I don't have that mod enabled. I'm also using the ELCP.