The currency unions which made it have all survived because they relied on a single monetary authority for managing the currency. Counter-intuitively, single currencies are often associated with complex political entities which occupy vast swathes of land and incorporate previously distinct -and often politically, socially, and economically disparate - units. The USA is a monetary union, as was the late USSR. All single currencies encountered opposition on both ideological and pragmatic grounds when they were first introduced. The American constitution, for instance, did not provide for a central bank. Many of the Founding Fathers (e.g., Madison and Jefferson) refused to countenance one. It took the nascent USA two decades to come up with a semblance of a central monetary institution in 1791. It was modeled after the successful Bank of England. When Madison became President, he purposefully let its concession expire in 1811. In the forthcoming half century, it revived (for instance, in 1816) and expired a few times. The United States became a monetary union only following its traumatic Civil War. Similarly, Europe's monetary union is a belated outcome of two European civil wars (the two World Wars). America instituted bank regulation and supervision only in 1863 and, for the first time, banks were classified as either national or state-level. This classification was necessary because by the end of the Civil War, notes - legal and illegal tender - were being issued by no less than 1562 private banks - up from only 25 in 1800. A similar process occurred in the principalities which were later to constitute Germany. In the decade between 1847 and 1857, twenty five private banks were established there for the express purpose of printing banknotes to circulate as legal tender. Seventy (!) different types of currency (mostly foreign) were being used in the Rhineland alone in 1816. The Federal Reserve System was founded only following a tidal wave of banking crises in 1908. Not until 1960 did it gain a full monopoly of nation-wide money printing. The monetary union in the USA - the US dollar as a single legal tender printed exclusively by a central monetary authority - is, therefore, a fairly recent thing, not much older than the euro. It is common to confuse the logistics of a monetary union with its underpinnings. European bigwigs gloated over the smooth introduction of the physical notes and coins of their new currency. But having a single currency with free and guaranteed convertibility is only the manifestation of a monetary union - not one of its economic pillars. History teaches us that for a monetary union to succeed, the exchange rate of the single currency must be realistic (for instance, reflect the purchasing power parity) and, thus, not susceptible to speculative attacks. Additionally, the members of the union must adhere to one monetary policy.