Where there are people who want to buy there will be people willing to sell, as innumerable tracts on black markets, drug dealing, and prostitution point out … The constant warfare of the archaic age of Greece, of the Janapadas of India, of the Warring States of China, was a powerful impetus for the development of market trade, and in particular for market trade based on the exchange of precious metal, usually in small amounts. If plunder brought precious metal into the hands of the soldiers, the market will have spread it through the population.9
