The limiting rule of the jobs is a good idea, but I would like to suggest a limited world (I.E. a 1500x1500 block world) so that some resources are Non-Renewable, thus providing an actual economy with supply and demands. This way i believe that factions will interact with each other more. For example if a faction own a vast majority of the iron in the world then other factions would be forced to barter, trade resources, or even forcibly take the resources from said faction. Also limiting of the world size would also cause there to be more interaction between people due to just simply being near each other. Rather then an economy driven by factions supplying themselves with the items they want/need, I believe that a closed world system would cause a true economy.Also of course as the world grows and some supplies are lost to deaths, machines built... etc. the world could be expanded again to include more resources.
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