The U.S. owes almost US$3 trillion to just Japan and China alone as it prints about US$696 million per day. According to the International Monetary Fund (IMF) or the worlds loan shark, China has even passed the U.S. as the worlds largest economy.
What I don't understand is why does the US own Japan and china so much? Why do they even need to borrow so much money when they can just print their own not to mention why would they want to be in so much debt that they can't ever really repay?
As regards to why not print rather than borrow money, the answer is that the US (wisely) prefers it that way, and pays enough interest on the debt to entice foreigners to buy debt.
Even with fiat money, debt is still one step removed from cash (ie less safe.) In a crisis, the US could decide to "honor" its debt by printing money to redeem it, or to abandon debt but protect cash, the core source of power of its elites.
This both gives the US more options at that (unavoidable) future moment, and slows down the financial pollution at present (since having to borrow money and pay interest slows down government profligacy and financial asset creation, as compared to printing money outright.)