I hope the developers will implement - or at least leave the possibility for modders - attrition in some tiles like deserts, tundra and snow. C-evo does that and the AI gets it. Of course, some civs should be exempt from it through UA promotions: on desert for Arabs and Mali/Songhai, on tundra for Russians, Mongols and Swedish. The same way a mountain range like the Alpes or the Himalaya are a geographical barrier, deserts and tundra should work. What do you think?