It owes most of it to its own citizens.

At some point in the past, the government needed to borrow money. Your grandma (for example) loaned it money with the promise it would pay her back in 10, 20, or however many years plus interest.

Loans to the government are very safe for the same reason you mentioned: it’s the most powerful country in the world and the chance it is still here to pay you back in 20 years is pretty damn high.

As such, loans to their own government are a huge part of citizens’ retirement plans, college funds, pension programs, insurance programs, you name it. It doesn’t pay very well, but it’s an extremely “safe” investment.

US citizens hold about 70% of all the federal debt in all these various forms. Theoretically, they could vote to forgive the debt and just never pay it back to themselves. Poof. Gone.

But good luck convincing grandma to agree to never get that money back. Especially when grandma votes. A lot.