In most previous civs, the biggest threats that you faced were external: barbarians, aggressive neighbors, and invasions. In civ 5 specifically, the only internal threats you face are unspecific "unhappiness" and gold deficits. I think that there should be more internal threats, like social unrest, protests over taxes, corruption etc. As it is right now, all you need to keep your people happy is to build the proper buildings. Historically, many empires collapsed because internal strife allowed external forces to get the better of them. Should these aspects be patched into Civ 5? Or maybe in civ 6. How would you want them to work?