I had no idea of this one. Did you know that Nixon on August 15, 1971 “closed the gold window and devalued the dollar.”
It was one of the rules or agreements of the Bretton Woods System that came out of the Bretton Woods Conference right after WWII in New Hampshire.
The chief features of the Bretton Woods system were an obligation for each country to adopt a monetary policy that maintained the exchange rate of its currency within a fixed value—plus or minus one percent—in terms of gold and the ability of the IMF to bridge temporary imbalances of payments. In the face of increasing financial strain, the system collapsed in 1971, after the United States unilaterally terminated convertibility of the dollars to gold. This action caused considerable financial stress in the world economy and created the unique situation whereby the United States dollar became the “reserve currency” for the states which had signed the agreement.