I think there are multiple explanations; here are some common ones: - When a country is completely modernized its growth tends to plateau; no good investments

I think there are multiple explanations; here are some common ones: - When a country is completely modernized its growth tends to plateau; no good investments left (in say infrastructure, health, education and so). - The Japanese Yen got too strong. Japan got stiffed at the plaza accord. After the 2nd world war it took 300 JPY to buy one USD. Today it hovers around 100. - Japan's skewed demographics. Too many elderly. Too few young. Little immigration. - Japan's conservatism. I.e big consumer electronics giants unable to transition into software companies. - Too much debt. Economy caught in a debt deflation / liquidity trap. - Competition from Taiwan, South Korea, China. - The big bubble was never allowed to pop and clear. Leaving zombie companies, slowly falling asset prices, bad debt for many decades ...