I am seeing the AI willing to sue for peace. I have mostly completed my first major war, playing Byzantium. Decided to conquer the Maya, who were my closest neighbor and strongest rival. They started suing for peace and offering cities and other big concessions fairly quickly (I think after I took one city and was starting to harass their capital), but I just ignored them until I had taken all of their cities on my continent. They somehow managed to survive though. At first I thought they had managed to get another city going (way before they could get across the oceans), then realized that I had the option on where you have to eliminate all their units too. They must have a scout or something running around somewhere I can't see. Either way, they made peace.
Back to the Huns...
I think some of you are downplaying their significance. They were around as a major player for much longer than 2 generations. We don't know much about their early history, but it must have been fairly substantial since they wouldn't have just emerged from a 'cradle of nations' as a fully-formed tribal nation that could sweep across Eurasia. People seem to be only looking at the time when they were invading Rome. Prior to that, they were displacing many other tribes, such as the Goths, which of course helped lead to the major barbarian wars and invasions that would weaken Rome by the time that the Huns actually invaded.
Other Civs, such as the Celts, were very significant and widespread, but never formed a unified nation or tribal alliance (except locally). The Huns also seemed to spend large periods of time in a dispersed state before forming larger tribal alliances / kingdoms. Both were very important, even if they look very different from our modern nation-state perspective.