First of all, if you ask how the exchange rates between currencies in the world are determined, there is no doubt that most currencies are basically determined by the free foreign exchange market. If the demand for a country's currency increases, the currency will appreciate and vice versa. The basic principle of this foreign exchange market is the same as that of the vegetable market. If you ask why the US dollar is the main currency for international settlement and how the status of the US dollar is formed, we should start with the Bretton Woods system. After World War II, in order to provide a stable financial environment for post-war economic development, the Bretton Woods system was established, with the US dollar as the gold standard currency and 35 US dollars exchanged for an ounce of gold as a fixed price. The currencies of other countries are linked to the US dollar, so that the trade between countries can be settled in US dollars, and the issuance of US dollars is more flexible than the production of gold. Therefore, when the trade of various countries needs a large amount of currency settlement, it will not be limited by the shortage of gold supply. If countries think it necessary, they can exchange gold from the United States at the price of $35 per ounce. The reason why the US dollar was positioned as the gold standard currency was because the US government had the largest gold reserves in the world at that time, accounting for more than 75% of the total official gold reserves in the world at that time.