Having a reserve currency is younger than the Great War.
(reserve currency = the ratio of ~gold to economic activity is unworkable for a metallic currency, but we have to use something as a reference.)
Lots of the current value of USD arises from its position as the global reserve currency. Losing the position involves losing that value, and it's unrecoverable, arising as it does from a history of conduct.
A disorderly loss of reserve currency status shall be a new thing in the world.