Had a game where all I had to do was kick them off my continent and then they capitulated. Did it like 5 times, and each needed me to take anywhere from 1 to 4 cities - as long as I had them off my continent, that's what I wanted, and they too seemed to realize being at war longer was pointless.
This may have been exacerbated by the fact that all of these civs had started out on my continent, and when I kicked them off, all they had left were their colonies on the other continent or islands, so their power was effectively broken and they couldn't have defended themselves against anyone else at that point.
It was funny, though. One of them, I thought he had only 3 cities on my continent, and I blitzed them and he still wasnt' surrendering, so I was trying to get transports lined up to get overseas, and then I spotted a city on the other side of the continent he'd apparently taken from someone in an earlier war. A few turns later I got enough force there to grab it and then "PLEASE DON'T KILL US!!!!"