The only thing keeping it up is there isn't anyplace else to put your money.
True but if you look at banks and their interest rates, the major banks are saying that most people who could are not putting their money in the market. The crash when it comes will not be that severe because too many people are sitting on the sidelines already.
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Put your money in solid functional goods.
Things like pickup trucks, large SUVs, plywood, fuel, iodine, guns, and ammunition.
Certain types of foods that are easy to store, but pleasant to eat are also a form of wealth with intrinsic value.
Nuclear war is unavoidable, and will destroy stocks and fiat currencies.