Collective Self Interest

Part of the difference between decentralization and citadelization lies in the layering of collective self-interest.  To be completely self-sufficient is nearly impossible and an unwise use of time and resources when compared with the camaraderie and security of gathering into a small tribe.  The Phalanx of ancient warfare was so successful because of its network effect of group attack and defensive shielding.  There is an ideal size for any organization based upon its purpose and it is only rarely a solo operation.