One thing I think would be cool to add to the game is low warmongering penalties at earlier Eras and higher ones as the game goes on. This would encourage earlier warmongering and make later warmongers truly hated, which is sort of how war is seen. For example (using fictitious numbers), warmongering increases by: 1/city conquered in Ancient/Classical 2/city conquered in Medieval/Renaissance 3/city conquered in Industrial/Modern 4/city afterward. In addition, warmongering penalties should decrease over time to keep early warmongers from being hated just because of what they did thousands of years ago. So if you manage to limit your wars than you shouldn't be hated by everyone else for the rest of the game.