I have become a convert to the last man philosophy. I will never go AI. Also, degree of aggression on my part depends on the circumstances. If the aggresor is someone I was trying to make peace with then but they attacked anyway, then I will do all I can to harm them and help their foes.
If it was a war that I instigated (something I do on ocassion
)that went sour - god forbid, I might even give my enemy my gems to help keep them in the race, since it always bothers me how turtlers or dogpilers have an edge over those who fight a fair one on one war (rare as those may be).
I think people underestimate how hard it can be to take a capital, so even when you have been knocked out of a game, you can still make it pretty tough for your enemy to capture the jewel of your nation - the capital - if you just stick it out. Too many people just go AI after losing a few provinces.
It can be fun just to see how long you can stay alive. And turns certainly are easy when you are down to one province.