People Waiting for Relief (Roosevelt Memorial Hall, Washington) There are various business cycle theories in the economics community. When analyzing the causes of the Great Depression, there are different opinions and no consensus. [1] Perhaps the best explanation of the cause of the depression is that the decrease in expenditure of one or several social groups exceeds the increase in expenditure of other social groups. In 1929, consumers purchased 72% of the gross national product, businessmen invested and consumed 18%, federal, state, and local governments in the United States used slightly less than 10%, and the remainder was exported. In 1929-1930, GNP spending fell by about $14 billion as investors and consumers reduced spending by about $15 billion. Although government spending increased slightly, the impact was insignificant. Reflecting the decrease in investment and consumer spending, layoffs and unemployment in the labor market increased, and business and industrial sales and profits fell. Based on the above analysis, it can be seen that as long as we find out the reasons for the decrease in consumer spending and business investment, we can determine the cause of the Great Recession. Through historical analysis, it can be clearly seen that in the 1920s, there were already several trends that were ignored or ignored at the time and were detrimental to economic development. Agriculture never fully recovered from the postwar depression, and farmers remained poor throughout this period. In addition, many of the so-called higher wage levels in the industrial sector are false. Within this decade, the introduction of new machines displaced large numbers of workers. For example, between 1920 and 1929, the total industrial output value increased by almost 50%, but the number of industrial workers did not increase, and the number of employees in the transportation industry actually decreased. Service industries, where wages are very low, have seen the largest increase in workers, which undoubtedly includes many skilled workers who have lost their jobs due to technological advancement. So statistics that show a slight increase in wages do not appear to reflect the true situation. Since workers and peasants are the basic consumers, economic difficulties encountered by these two groups of people will definitely have an impact on the consumer goods market. Under these circumstances, the expansion of advertising and installment credit sales of the twenties had undesirable consequences. Installment credit sales strive to expand the consumer goods market. From 1924 to 1929, installment sales increased from approximately $2 billion to $3.5 billion, which shows that the growth rate is astonishing. There is no doubt that the use of installment credit sales has increased the sales of durable consumer goods such as cars, radios, furniture, and household electrical appliances. However, the popularization of the installment sales method also shows the fact that without increasing loans, the consumer goods market cannot accommodate the large number of products produced by the industrial sector. Moreover, from an economic point of view, this method of selling and lending itself carries certain risks; as long as consumer credit, that is, installment credit sales, is reduced, consumer purchases are likely to decrease. It seems that this happened in 1929. The expansion of industrial production in the 1920s was due to huge investments in new factories and new equipment. This investment has enabled the employment of a large number of workers in relevant sectors such as construction, machine tool manufacturing, and the steel industry. Therefore, capital expenditure or investment