https://github.com/libbitcoin/libbitcoin-system/wiki/Qualitative-Security-Model

"For any period of time, economic security is a function of the number of merchants and the similarity of amounts traded. The strongest economy would be all people in the world trading for the same number of units in the period, an ideal which can be called a "distributed" (or fully-decentralized) economy. The weakest would be one delegate accepting all units traded in the period, which would be a "centralized" economy."