Legal Tender Era

With the creation of central banks, currency underwent several significant changes. During both the coinage and credit money eras the number of entities which had the ability to coin or print money was quite large. One could, literally, have "a license to print money"; many nobles had the right of coinage. Royal colonial companies, such as the Massachusetts Bay Company or the British East India Company could issue notes of credit—money backed by the promise to pay later, or exchangeable for payments owed to the company itself. This led to continual instability of the value of money. The exposure of coins to debasement and shaving, however, presented the same problem in another form: with each pair of hands a coin passed through, its value grew less.
The solution which evolved beginning in the late 18th century and through the 19th century was the creation of a central monetary authority which had a virtual monopoly on issuing currency, and whose notes had to be accepted for "all debts public and private". The creation of a truly national currency, backed by the government's store of precious metals, and enforced by their military and governmental control over an area was, in its time, extremely controversial. Advocates of the old system of Free Banking repealed central banking laws, or slowed down the adoption of restrictions on local currency.
At this time both silver and gold were considered legal tender, and accepted by governments for taxes. However, the instability in the ratio between the two grew over the course of the 19th century, with the increase both in supply of these metals, particularly silver, and of trade. This is called bimetallism and the attempt to create a bimetallic standard where both gold and silver backed currency remained in circulation occupied the efforts of inflationists. Governments at this point could use currency as an instrument of policy, printing paper currency such as the United States Greenback, to pay for military expenditures. They could also set the terms at which they would redeem notes for specie, by limiting the amount of purchase, or the minimum amount that could be redeemed.By 1900, most of the industrializing nations were on some form of gold standard, with paper notes and silver coins constituting the circulating medium. Governments too followed Gresham's Law: keeping gold and silver paid, but paying out in notes.