National debt.

[JustLetOneOff]

If most countries ,if not all of them, have a national debt who is in credit? Where do governments borrow money from and what happens if they can't or refuse to pay it back?

[gryffron]

Pension funds. Banks. Other governments.

What happens if they can't pay it back? It evaporates. Gone. Back where it came from, which is nowhere.

Money isn't real. Money is just a measure of faith, belief. Belief in its future value. That's why we can have inflation, when faith in money reduces. That's why currencies change in value wrt each other, because faith shifts from one to the other.

Governments can create more money anytime they like. Printing banknotes, or electronic QE. But do it too much and you erode that belief in its future value. Borrowing rather than creating can help to sustain the belief.

To fully understand the answer to your question, you need a much better understanding of what money really means and how money really works.

Gryff