On June 13, 2023, Janet Yellen, former chair of the Federal Reserve and current Secretary of the Treasury, suggested that people should expect a gradual decline in the US dollar as the reserve currency. Although this is a rare moment of directional accuracy for Yellen, who is correct to imply that the dollar's days as the world's reserve currency are numbered, history shows that she is incorrect to suggest the decline will be gradual.

Currency declines tend to happen gradually, then suddenly. Once a critical mass anticipates a future devaluation of their savings (which may have been happening "gradually" up until that point) there is a mad rush to the exit. Everyone hurries to exchange their currency for something of intrinsic value before the next guy. This sends the prices of goods soaring and drives the currency's value lower. Inflationary fuel is then added to the fire via government debt monetization. As the process above unfolds, sectors of the economy fail, the tax base collapses, and government obligations cannot be fulfilled. Politicians then turn to the printing press in a desperate attempt to "stimulate" the economy into recovery. The vicious cycle continues until citizens finally abandon the failed monetary unit and adopt a new form of money.

Here are some of the most historic cases of hyperinflation over the last century that transpired gradually, then suddenly, with total currency collapse taking a year or two at most.