The "Roaring 20s" that followed the end of World War I was a period of prosperity for most Americans. As the economy grew, stock prices soared. By the end of the decade, as many as 25 million Americans had placed money in the stock market in order to share in the wealth. The best part of the process was that you didn't need a lot of cash to join the party. You could buy your stock on margin. That is, borrow the money for your stock purchase using the value of the stock itself as collateral. It is estimated that by 1929, the total amount of debt amassed by the practice had reached six billion dollars. It was a house of cards that remained erect as long as stocks continued to increase in value. However, if stock prices plummeted, the whole rickety structure could collapse.