The US Federal Government, runs a budget deficit, it spends more than it earns.
To fund this gap, it issues T-Bonds (Treasury Bonds), debt issued by the US Treasury to bridge the gap between income and expenditure.
The US National Debt is huge.
As you can see over $18 TRILLION is owed by the US Federal Government.
Over $6 Trillion is owned by foreign investors. What this means is that foreign investors are the creditors to the US Government.
So when you look at the $6 Trillion, this is over 30% of total US National Debt is held by foreign investors.
China owns the biggest chunk of U.S. foreign debt at $1.3 trillion, followed by Japan at $1.2 trillion. Just these top two creditors constitute a huge portion of US Debt.