I'm a nice guy, really. I usually don't start wars. Very early in the game (usually before Chivalry, ALWAYS ALWAYS before Invention) I'll blitz a small rival nearby. They usually only have about 5-9 cities around then. I always wipe them out and take their place of I attack at all. Otherwise I don't spend hardly any effort on a military (1 or 2 defensive units per city) and wait (sometimes hope) that I'll be attacked.
I don't usually start wars. Sometimes, very early in the game (before Chivalry), I'll blitz a nearby neighbor into oblivion. Other than that, I usually spend little effort on a military until I'm attacked by Vikings or whatever. Then I set an objective and go for it. (ie, attacked by Persians just the other day so I resolve to use my excessive productive might to Battleship/Cruise Msl their units to death. Then I capture a few cities by helicopter so I can get peace.)