In 1929 people in stocks and industries were trying to sell more than could buy. When people were not buying the products, the banks, and companies who invested in the stocks went bankrupt leaving people with no money.
The great depression happened when the stock market crashed and no one was getting paid. Since no one was getting paid people could not afford rent for housing so, people were making tiny shelters with scrap wood and metal. People called the tiny shelters Hoovervilles as a mockery towards the then president Herbert Hoover.