It has been in use since the old days when vessels were really slow comparing to modern container carriers.
Even in 19th centuary, especially shipments from South America to Europe or Africa to Europe took quite significant time.
Long transportation periods create financial problems for both exporters and importers as finance has always been a key issue for international trade.
International traders and banks managed to find a brilliant solution for this problem.
They started to implement a payment method which is called letter of credit.
Under a letter of credit payment method, an issuing bank notifies its conditional payment undertaking to the seller in a written format which means that issuing bank sends a letter to the exporter which contains the conditions and requirements of the payment.