Causes of the Great Depression
Second, there are the monetarists, who believe that the Great Depression started as an ordinary recession, but that significant policy mistakes by monetary authorities (especially the Federal Reserve) caused a shrinking of the money supply which greatly exacerbated the economic situation, causing a recession to descend into the Great Depression. Related to this explanation are those who point to debt deflation causing those who borrow to owe ever more in real terms.
Depression (economics)
A long-term effect of the Great Depression was the departure of every major currency from the gold standard, although the initial impetus for this was World War II (see Bretton Woods Accord). In any case, the world economy has simply outgrown the capacity of additions to the world gold supply to accommodate the increase in world population and increased trade without periodic, painful revaluations of any currencies tied to gold.