What effort are you talking about? Conquering level 5 or level 10 flat? I do it hundred times a day and if you think it requires any effort, you probably choosen wrong game. I made lots of npc around and never was worried about making lists of npcs i made. I simply farm any npc i can reach and if i see level 10 flat anywhere around i make an npc there. If i see anyone farming npcs near my city, i will simply estimate the time of the attack by looking at the amount of resources left and next time will farm that npc earlier.
For level 5 npc i would simply farm them every hour and anyone else would have to go farm another npcs elsewhere.
Sometimes i move my cities to another regions for attacks, then i farm any level 10 npc with resources if i need food urgently and can't attack my enemy for some reason or if he already have no food. In that case if i receive email from friendlie with whining about npc, i will ignore it, if it will be neutral or enemy, i will attack him. I hate any stupid complains about npcs. When you click 'Abandon' and type your password for confirmation you agree that you no longer need that city! full stop! NPC belong to noone. farm my npc if you can and dont complain if i farm 'yours'.



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