Take, for example, the late 18th century and pre-French Revolution. The American War of Independence (1775 - '83) and the Seven Years War (1754 - '63) were financially ruinous for Louis XVI's France, due to his knack of borrowing large sums of money to fund these wars, leading to greater expenditure than income, and therefore deficit.
How was money transferred in times like these? There was no such thing as digital transactions, and surely the sums of money would have been far too large to physically transfer. Could it be that when one borrowed money, it was more of a statement of 'we have this much money', so long as there was proof that those who borrowed it had the money to spare?