The Ascent of Money
The word 'credit' stems from 'creed' or 'credo' which implies trust.
Around 1200 AD, Fibonacci's book 'Book of Calculations' suggested the use of Arabic numbers in business transactions. Since at the time Roman numbers were used which proved ineffective in dealing with arithmetic.
The concept of loaning money with interest existed but was only practiced by the Jews since their religion allowed lending money to people of other religious persuation; while this was regarded as a sin by the Catholics. These Jews would live in congregated areas, like gethos, and it is there they would sit on their special purpose benches doing their dealings. The word 'bank' stems from these benches.
Then during the Renaissance there was the infamous 'Medici family'. While many of their first offsprings were outlaws and often ended up in jail, they however became very influential, even to the extend that they helped 'shape' the Renaissance. Their forte was money exchange between cultures. The profits raised from that was a form of compensation for the work to achieve this currency exchange. While interest is in essence compensation also, the Medici family managed to make earning money with money socially acceptable. The true concept of banking started around this period.
From then on 'loansharks' started to appear. These were people that loaned you money for you to pay back at a great cost. They often had to use threats and could demand 'flesh' if a loan was not repaid.
Currently America has run a debt equivalent to $35,000 USD for every man woman and child in America.