The depression really didn’t get going until the major bank failures in 1930. Roosevelt started Making Depressions Great Again after taking office in 1933.
Democrat Secretary of State William Jennings Bryan had stated (Hearst’s Magazine, Nov 1923):
“The Federal Reserve Bank that should have been the farmer’s greatest protection has become his greatest foe.”
There were a bunch of mistakes that led to the Great Depression. In no particular order:
The use of margin purchases in the stock market. This has more recently been duplicated these days with sub prime housing mortgages. People with a dime could buy a dollar of stock, as long as they promised to eventually pay the other 90 cents. Gambling.
The physical market was horribly price deflated. Prices were low because there was no money to buy things.
Hoover tried to fix things from the top down. This doesn’t work when people on the bottom are starving, and can’t wait.
Even with the Dust Bowl wiping out thousands of farms, there was still far too much food for people and animals, so the bottom dropped out of the already low price for food.
There was no international buffer because of the international depression.
This occurred despite the existence of the Federal Reserve which was created with promises that it would prevent financial panics.
Actually, the FED kept track of the money supply without taking into account the impact of the newly popular checking accounts, and thus inflated the actual money supply. When they discovered the mistake, they secretly began to buy the Federal Reserve Bonds needed for banks to make loans, thus reducing the money supply, even though gold was arriving from Europe (the gold standard required countries receiving gold to reduce their interest rates). This caused the depression in Europe (less gold, less money supply in Europe), eventually bit enough to collapse our stock market, and caused rural banks to not make loans to farmers to plant their crops; this in turn led to foreclosures of farms. The Fed continued to reduce the money supply throughout the Roosevelt’s New Deal, which tried to increase economic activity while the Fed was reducing economic activity.
Proof of the above lies in the “Monetary History of the United States, 1913 - 1939”