The Kielburger brothers always write interesting and informative articles on many international social issues. Here they've written something different from their regular articles, as their latest article is about the relationship between China and the US which binds them more tighter than many would think. Specifically this is referring to their economic trade relations in which China has a huge surplus with the US, exporting more to the US than importing, while also buying up a lot of American treasury securities.
As the authors note:

"China is now so deeply invested in U.S. securities, any disruption to the value of the dollar would be a serious blow to its own reserves. Reliant as they are on the U.S. market for goods, the Chinese are forced to buy up new securities as soon as they're issued to prevent their currency, the yuan, from appreciating against the U.S. dollar. Neither country holds a significant advantage over the other."

The thing is not only does China depend on the US to buy a lot of its products, but it also needs the US to keep a strong economy and currency in order for its own vast holdings of American treasuries to maintain their value, to the point of propping up the US currency by continuously buying up American treasury securities. In essence, the US has little leverage over China.

Of course, China does realise the vulnerability of their situation and raised some concerns by suggesting selling off some of their US dollars last year which they later retracted. They have also tried to invest in more US-dollar non-treasury investments such as Morgan Stanley.
See this table for the list of foreign countries who own American treasury securities. As you can see, China is by far the number two owner though it is relatively a little behind Japan. Keep in mind Japan's economy is greater than China's.