> how this all happened?

Turkey elected a strongman. He used the state to buttress his own power. That made necessary, but politically-difficult decisions (like raising interest rates), impossible.

> Turkey has external debt but so on the US

Few Americans borrow in non-U.S. dollars. And the U.S. government only borrows in U.S. dollars. This works because the dollar works. Investors and exporters trust it to retain value.

The lira, on the other hand, isn't trusted. So when the Turkish government wants to borrow money, investors aren't willing to accept being paid back in lira. (And the government, in any case, needs hard currency to pay for imports. Because the people selling Turkey imports don't want to be paid in lira, either.)