This is my favourite one.
I borrow money from you to spend on whatever I like. When the time comes to repay my debt, I borrow more money. From you. To repay my earlier debt to you. And you accept it, because you know I will definitely repay my debt to you. I have your full trust that I always keep my promise.
My debt to you keeps growing bigger and bigger as the years pass, but you still keep lending me money to spend however I like, because you know I always repay my debts. I always have.
Now replace ‘I’ with the U.S. central bank, and ‘you’ with all the countries in the world.
https://www.quora.com/What-is-best-financial-scam-still-in-existence