Surprised nobody has mentioned the fact that 401(k) funds are often invested into a US index fund, and nobody can guarantee the past trend of exponential growth

Surprised nobody has mentioned the fact that 401(k) funds are often invested into a US index fund, and nobody can guarantee the past trend of exponential growth in value will continue. As an example of such a disturbance, consider the Japanese Nikkei market index which still hadn't recovered from its crash in the late eighties. The US as a world superpower could very well be at its peak, marking the beginning of a never-ending decline, much like the Roman Empire, the USSR, the Mongol Empire, etc. That's probably the riskiest thing about a 401(k) fund IMO, much more than possible increased future taxation. As an aside, I really start to worry given the ongoing American brain drain. We're discouraging skilled immigration while simultaneously condemning domestic gifted education and making university degrees cost prohibitive. Other countries see this and laugh as they begin to run laps around us.