The dollar is the world currency. Oil is pegged to the dollar. All modern equipment, agriculture, daily necessities and automobiles need oil. Why the United States can dominate the world is simply dollar hegemony, and the essence of dollar hegemony is oil. This is also why the United States has always waged wars in oil-producing countries in the Middle East, just for oil. Therefore, all countries have to earn dollars, sell cheap goods to the United States to earn dollars, and there is a certain amount of dollars, which is linked to oil production and cannot be exceeded, otherwise it will cause inflation, so the US dollars will be less and all will flow abroad. In order to keep enough dollars in the United States and prevent deflation, there must be a mechanism to return dollars to the United States, and this mechanism is US Treasury bonds.

US Treasury bonds are the most liquid and reliable in the world. It can be traded on the Wall Street Exchange at any time. Other countries have so much money besides buying oil, and some of this money will be used to buy US Treasury bonds. If it is not suitable, it can be realized at any time, which is very convenient.