I don’t really understand your question
A. 200 years of stability
I believe the answer is "change to meet the needs of a modern society".
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Stagflation, price control. Keynesian policies were failing. The oil
crisis showed the stupidity of price controls. The stagflation showed
that an increase in the money supply does not increase wealth.
In the 70s we still had Vietnam, we had Nixon, there was Watergate,
Gerald Ford, Paul Volcker raising interest rates to 20% in the Federal
Reserve, government bailing out Chrysler. </span>