This section of Smith's theory attempts to describe the timing of the process of gentrification. At the end of a period of expansion for the economy, such as a boom in postwar suburbs, accumulation of capital leads to a falling rate of profit. It is then favorable to seek investment outside the industrial sphere to hold off onset of an economic crisis. By this time, the period of expansion has inevitably led to the creation of rent gap, providing opportunity for capital reinvestment in this surrounding environment.