The British Pound Sterling lost its status as the primary basis of global trade in 1944. Why? Because the Treasury of the United States held title to about 4/5ths of the world’s officially-held gold reserves [more than 20,000 tons after WWII]. The dollar became the world’s “reserve currency” because U.S. government creditors could convert their dollars to U.S. gold [from 1792 until Aug. 15, 1971].
Since gold convertibility was suspended in 1971, the U.S. dollar has retained its “reserve-currency” status because of the dollar’s forty-year monopoly in settling OPEC oil trades [the “Petro-Dollar” system].
After the 2007 credit-collapse, China began to implement a strategy to slowly ‘de-peg’ from the petro-dollar and aggressively* add gold to its foreign exchange reserves.