Well, an archaeologist studies bones.
Along with the diminishing supply of metals used for currency, Chines scholars developed the new economic idea that held paper money as a means of payment and exchange, not as a value in itself. The issuing of paper currency in Song China was as much of a process as the invention of paper currency itself.
Answer:
One of the main arguments used to support US military involvement in Vietnam was the fear that if Vietnam fell to communism, other nations in Southeast Asia could as well.