The Economist had a good article, that featured the Euro. The background to establishing the Euro was done by a CDN Noble Prize economist. Basically to replace the US dollar as a Reserve currency and World Currency, has many difficulties. There has never been to many examples of a World currency or a freely exchangeble currency in the world that was not backed by a dominate nation. World currencies are usually the currency of the exsisting world power. Creating a currency that is not backed by a nation, (SDR's) or even the Euro has it's difficulties. Not being a world power doesn't limit it's currency, but it helps. Many powerful nations in the past (Dutch), were great commerce nations, but backed this up with a strong naval presence. The Dutch salied up the Thames and shelled London. The English had enough of the Dutch, and reverted back to their traditional enemies the French. It was the international commerce of the Dutch that made their currency, the Guilder, freely exchangable over most of the world. The transition from one great nation, and it's currency to another, is a reflection of time, and it's value. As these nations faded, their currency faded, resulting in the markets,(international traders) using other currencies to do business. There was No law enacted in the past it just was a slow gradual change. The Spanish at their peak had huge inflation problems, mainly because of vast gold wealth entering their country.This basically eliminated the Spanish currency from taking a competeing international role. Similar problem facing the US dollar today, but their is NO competeing nation or competing currecny to step up to the plate.The US dollar is almost the sole world currecny and reserve currecny, while in the past before the rise of the British Empire there was competing forces.With the slide of the Brits, America was the natural replacement, but today we're at a stall point.. No replacement. The use of a single currency backed by a single nation is now our downfall. The US problems are now the world's problems, and the US has GOT PROBLEMS.The cure is a single currecny, (UN currency) backed by the entire world of commerce, or several currencies (3 or 4) that all play a role in interational commerce and trade. Here's the problem, until the world sorts it out, with a plan "B", there is a growing chance that the US dollar(with it's problems) will cause a world destroying event.