I get that a single currency is problematic. Arguably it is problematic even in the US, after all this time. But it doesn't necessarily follow that a single currency is fundamentally infeasible. The US isn't crippled because of it.

By contrast, the poster gave a very concrete explanation why adoption of the Euro by the UK was [then] infeasible.

The US is at least somewhat willing to tax money made in California and spend the takings in Michigan. Greece or Italy gets the worst of both worlds: they can't devalue their currency to make their industries competitive with Germany, but they don't receive much share of German taxes either.

In Europe you have tens of countries that speak different languages and have cultures that go back 1000-2000 years. That, along with a bunch of political baggage and that each nation has its own fiscal policy, and the starting points between EU and US are very very different.

I would instead extend your concession that given the single currency already exhibits creaks in the US, imagine how hard it would be to manage in the EU.

Germany, for example, is the descendant of the 19th century North German Confederation, a Prussian-dominated customs union between north German states, which in itself was an effort to recreate the earlier German Confederation without involving those pesky Habsburgs.

The Holy Roman Empire was a unified confederation of German, Italian, Swiss, and Bohemian states that allowed large amounts of autonomy and sovereignty within its borders. In fact, our modern conception of sovereignty dates from the Peace of Westphalia, which ended a thirty-year-long war (imaginatively named the Thirty Years War) fought largely over the authority of, once again, those pesky Habsburgs to tell HRE member states what their state religion should be.

Britain was formed by the unification of England and Scotland, both of which are still legally considered separate countries under British law. Italy was formed as a union of Italian states, largely from an effort to overthrow Habsburg rule. Spain was formed as a union of Iberian kingdoms (that eventually fell under a branch of the Habsburg dynasty which went extinct due to inbreeding, leading to a war of succession.) Poland and Lithuania had varying degrees of unification from 1385 until 1795, when the then-unified country was torn into pieces and partitioned off into their surrounding empires, including Habsburg Austria.

So really, given European history, it seems like most European countries don't really have a problem joining together into larger unions, so long as those unions aren't ruled by Habsburgs. The closest the EU ever got to that was when Otto and Karl were Members of the European Parliament up until 1999, so hopefully we're fine.

The EU is a complex institution and the single currency is only part of it. An integral part, to be sure, but IMO we (the political chatter class) put far too much emphasis on monetary policy, both as our source of problems and a source of solutions. Often it's a distraction or excuse for more substantive issues, like political and fiscal ineptitude. Take Greece for example--when push came to shove most observers, as well, as Greeks themselves, decided that leaving the Euro was not the answer. When forced to soberly assess the situation it turns out that the Euro wasn't the most pressing problem and that on balance they were better off enduring.

Regarding comparison with the United States, let's not forget that political battles over a national bank dominated national politics for almost the first 50 years. Similar to issues over tariffs, what benefited the north was often to the detriment of the south, and vice-versa. And this was at a time when there were virtually no direct federal wealth transfers, and federal revenue came predominately from tariffs, which pitted not only the north (net importers) against the south (net exporters), but both against the federal government (tariffs were placed on both imports and exports). If the interplay between monetary policy and trade competitiveness was understood at the time and today's Euro critics were teleported back in time, who knows what might have happened!

The point about other European countries is well taken and I believe there have been talks to get some countries out of the Euro zone. In part this is a big deal because countries like Germany don't want to prop up countries that are in financial difficulty. They have no controls for dealing with these problems and the result is that you need cash infusions from the EU to keep it all swimming.

But that's really the point, isn't it? How much of a "Union" do you want? It even gets to the heart of why some people want Briton to leave the EU.

Which countries was the Euro "completely infeasible" for, and what are the facts demonstrating this statement is true? It's a very strong assertion.