It is a common ground for exchange of value. In the beginning, there was no difference between money and wealth. In early trade, an exchange rate between commodities was created, such as one chicken for a piece of paper in England, which fluctuated wildly. Copper, silver and gold were soon adopted everywhere as exchange media with rates against the local money. Money has always been based upon that confidence.
Money is ten thousand years older than states.
Paper money was nothing other than a transferable bill of exchange. It could be used the way we use bank checks today, but it was far more unstable. The problem with paper money was that the person with the printing press could publish it, which vastly increases the money supply, without producing real wealth behind it. Inflation is the consumers version of a no confidence vote in the sovereign publisher. After 1492, the possibility of reducing trade was nil, because for the first time in history, humanity was experiencing variety in foods, spices, perfumes, clothing, ceramics, home heating, furniture, the works.