The Great Depression started in 1929 and carried on during the 1930's it caused most Americans to realize that buying on margin had its problems, besides being a great way for brokers to rip off unsuspecting immigrants...or very ignorant, naive Americans. The depression spread to Europe and the rest of the World. In Germany, Nazis came to power because people were desperate due to the depression.
The present Economic crisis started in a similar way. People in many parts of the Developed world bought too much on credit till confidence collapsed. Hopefully economists understand more today and the crisis won't become so extreme. We don't know yet.
Many conservatives say that Roosevelt's New Deal did not help relieve the Great Depression. This however is false as it cut Unemployment from 20 percent to 10 percent. However unemployment went back up because FDR decided to listen to a conservative for once because he was open minded. After listening to him Roosevelt decided to cut down on the amount of money that was put into his government spending. Unemployment then started to rise. That shows how well conservative economics works.
Roosevelt also started a Social Security system which helped relieve some of the worst Poverty for Americans.
Later World War Two did help end the Depression. Conservatives say this proves Liberal economics fail. Thats untrue, as World War Two caused the US government to spend massively on the military. Their argument basically "the massive government spending of the New Deal didn't end the Great Depression, the massive spending of WW II did!".
The other major mistake conservatives make is thinking all Roosevelt's New Deal Programs were Social Programs. A major part of New Deal legislation was the imposition of business and financial regulation and enforcement, intended to protect and reassure investors. Roosevelt's actions to help and reassure all nations citizens and give them all renewed hope to access the American Dream stood in stark contrast to the actions of his predecessor.