A few turns after the warning it would arrive, it came and stood over my capital. It slowly (very slowly) knocked on my walls, then continued to siege even after the walls were down. It never tried to storm my city at all. Eventually I bought it off and I think it has stopped attacking but it hasn't actually gone away or offered me the chance to suggest which of my foes to target. Is this a bug? If it isn't then it rather makes this terrible threat underwhelming. And since it hasn't gone away my city is still under siege so it looks as if I will have to try to kill it after all because my capital being under siege is not helping my economy. I did try and fail to beat it in combat a few turns ago,