Short answers, pulled from the story.
Alfred Marshall published Principles of Economics in 1920 to define the term commodity as a general economic good. The text states that markets treat instances of these goods as equivalent regardless of who produced them.
Karl Marx described fungibility by stating that from the taste of wheat one cannot tell who produced it. He argued that exchange value arises from socially necessary labor time required to produce a good.
The first commodity super cycle started in late 1890 and accelerated on the back of U.S. industrialization. World War One drove prices higher before they peaked in 1917 and entered a downtrend to the 1930s.
Companies like Vitol and Glencore trade these items globally without regard to specific producer identity. A list of companies trading globally descending by size as of the 28th of October 2011 includes Cargill and Trafigura.
Soft commodities are goods that are grown such as wheat or rice while hard commodities are mined resources including gold silver helium and oil. Energy commodities include electricity gas coal and oil.