China has frequent trade with the United States, and the United States is China's second largest trading partner (the largest is the European Union). Our country earns a lot of dollars by exporting products to the United States, such as socks, tires and clothes, and these dollars become foreign exchange reserves. In fact, China's foreign exchange reserves are so huge that the only thing it can buy is US Treasury bonds, which is an investment. Americans didn't force us to buy it.
National debt, also known as national debt, is a creditor-debtor relationship formed by the state on the basis of its credit and in accordance with the general principles of bonds. National debt is a bond issued by the state, a government bond issued by the central government to raise financial funds, and a debt certificate issued by the central government to investors, which promises to repay the principal and interest within a certain period of time. Because the issuer of national debt is the country, it has the highest credit and is recognized as the safest investment tool.
References:
Baidu encyclopedia national debt web page link