
Inflation is a monetary phenomenon. The more money, the more inflation. That's why inflation is commonly described as "too much money chasing too few goods."
Milton Friedman won a Nobel Prize for proving what had been obvious to everyone before the 20th century--that rising prices were a function of more money.
Mo' Money. That's why bouts of inflation followed discoveries of gold and silver--or sudden influxes of gold and silver, as when the Spanish conquered Mexico and Peru in the 16th century, which lead to a trebling of the price level in Spain and a generalized inflation across much of Europe during that century.
Spaniards thought they were rich after conquistador-ing all that gold and silver, and it was, but it blew through all that money on vainglorious foreign wars, while neglecting to increase agricultural and craft production ("industry" wasn't really an idea yet) in the homeland. Spain had too many Don Quixotes, and not enough inventors and tinkerers.
This site here, The Big Picture provides a great overview of the relationship between money supply and the price level.
As anyone can see, the relationship is close, indeed. And so back to that St. Louis Fed chart, showing the monetary "hockey stick."


