I typically play peaceful and don't have much of an army but I still need to be prepared to defend against any aggression, particularly after ideologies. What's the right balance between air units, anti-air units, ranged, and melee units? Are nukes an effective deterrent to aggression? Post gatling gun, is artillery the better ranged unit to build from a defense perspective? From an anti-air perspective, are planes or ground units the better choice. Obviously I'm trying to keep my forces as small as possible to save on upkeep but don't want to invite attacks.