Thanks for the responses guys. I was hoping for something easier than a dome, as they are hitting me in a lot of different provinces, but I guess I will concentrate them in one or two and cast domes. I've had this happen to me when I was playing Neifel and Lanka, but no real problems arose from them (GoH was active in both cases). This time, however, I am in the early game and have been getting hit by them pretty much since the game started. What a pain.
Humans are just too "squishy".