What were the main causes for the roaring twenties?

There were various aspects of the Roaring Twenties.  First, the 1920s did not "roar" for all Americans.  After the war in Europe ended, demand for American foodstuffs abruptly declined, which meant falling commodity prices.  Farmers went into debt before 1920 in order to by machinery and more land, and the lower farm prices meant that many of them lost their homes.  The 1920s also did not roar for Eastern European immigrants since Americans were afraid of the Bolshevik menace.  Many were tried unfairly as being Communist sympathizers and deported on the Buford, which was called in the newspapers the "Soviet Ark."  A. Mitchell Palmer, U.S. Attorney General, led the prosecution of these people. 
The 1920s were a time of rebellion.  Women got the right to vote and since many of them were able to work outside the home during the war, they sought more rights.  They began to dress like the "flapper" with shorter dresses.  Women also smoked and drank in public, which twenty years before would have been taboo.  Prohibition and the Volstead Act made alcohol illegal, but the federal government did not have the means to enforce this law, and many ordinary citizens who were otherwise law-abiding drank.  After the recession of the early '20s, wages and the stock market improved, and workers had more disposable income and leisure time.  They bought things such as cars and radios on credit, and this created a culture that thrived on entertainment.  This is probably the part of the '20s that people say "roared," as the family vacation, "talkies," and syndicated radio shows became popular for the first time in American history.  The main cause of the Roaring Twenties was the disposable income levels after WWI and Americans felt like they could relax.  There were also signs that morals were changing as a generation of young men returned from Europe with interests in psychology and science being their guides more than conventional Christianity--church membership dipped slightly during the 1920s.