If you had reinvested your dividends, you'd have gotten your money back by the end of the war (and you'd only have lost 1 or 2% approximately six years later).
35 years later you would have an annual return (inflation adjusted) of 6% (6.5 times as much as you put in).
And this is somebody who invested in the absolute peak of the market in 1929, and then saw the worst crash in history, followed by the worst war in history.
1) Shares were massively overvalued compared to their yields. E.g. if P/E ratios were 50:1 then I wouldn't buy the market
2) There's a fundamental issue in the economy. Plague, war, asteroid, climate change. Whatever the issue, you probably have bigger things to worry about than your retirement fund, and you have no better bets to place
The stock market is just made up of businesses. Businesses make money. Owning part of a business gives you a return. There's no magic to it, no massive extrapolation based solely on past performance. If you think there's a decent chance businesses aren't making money, then you ought to become a prepper.
35 years later you would have an annual return (inflation adjusted) of 6% (6.5 times as much as you put in).
And this is somebody who invested in the absolute peak of the market in 1929, and then saw the worst crash in history, followed by the worst war in history.