Since the end of World War II, the US dollar has been the world's main reserve currency and has played a central role in the international monetary system.

During the gold standard period and later during the Bretton Woods period, international trade was generally conducted using currencies convertible into gold or US dollars.

In the gold standard system, the currencies of the participating countries were fixed at a fixed exchange rate against gold. International payments were made in gold, which meant that countries could convert their currency into gold at any time at the fixed exchange rate.

During the Bretton Woods period, countries pegged their exchange rate to the US dollar, which itself was pegged at $35 per ounce of gold. International payments were made in US dollars, which could be converted into gold by foreign governments at any time.

The US dollar became the world's main reserve currency during this period, as gold was difficult to acquire and other countries were willing to accumulate reserves of US dollars to facilitate international trade and to protect their own currencies against fluctuations. change. US dollars were considered a stable and reliable reserve currency, backed by convertibility into gold.

The dollar was more and more solicited and the United States produced more of it to satisfy the demand.

At one time the United States had more dollars in circulation than gold in reserve, a serious problem for the United States if the countries came to require the exchange of the American dollars in their possession against gold.

So in the 1960s, the United States therefore experienced a significant increase in their trade deficit and their balance of payments. Investors began to worry about the ability of the United States to maintain its fixed exchange rate with gold, which put pressure on the dollar.

In 1971, US President Richard Nixon announced that the dollar would no longer be convertible into gold. This marked the end of the gold standard and allowed the United States to have control over the value of the dollar according to world demand. But it should be remembered that since the dollar is no longer backed by gold, the countries have gotten rid of most of their dollar, and the dollar has lost more than 90% of its value.

To avoid the total collapse of the dollar in 1970, the United States established the petrodollar system. The petrodollar is a system in which crude oil was traded exclusively in US dollars, reinforcing the dollar's position as the world's main reserve currency.

Since the 2000s, emerging countries have therefore begun to diversify their foreign exchange reserves by using other currencies, such as the Euro and the Chinese Yuan.