The following commentary comes from an independent investor or market observer as part of TheStreet's guest contributor program, which is separate from the company's news coverage.NEW YORK ( TheStreet) -- By the mid 1980s economic forecasts were clear -- Japan would soon be the world's most powerful economy. But that never happened. Japan's stock index, the Nikkei 225, closed 1989 at 38000. Today, 23 years later, the Nikkei sits at 9600 -- a 75% drop. There are myriad reasons for Japan's economic collapse. But, Henry W. Dent of the HS Dent Foundation claims that there is a near-consensus among demographers that the root cause of Japan's inability to recover has been its demographic collapse. Between the end of World War II and 1950, Japan's fertility rate (i.e., the number of children born to one woman) was 4.5. By 1989, that fell to 1.6. Today's fertility rate is 1.2. A fertility rate of 2.1 is required to maintain the population.