American and European Unions, Compared(1)
The (1648) Treaty of Westphalia created the modern nation-state by limiting sovereignty to fixed boundaries. Soon, everyone had a sovereign King. While there had been kings for centuries; what was new was kingship boundaries. Inheritance addressed succession, but nations outgrew the ability of one man to rule it all, so aristocracies evolved into republics, republics into semi-democracies, finding succession still had difficulties.
Today, Europeans live in republics, wishing to unite into democracies, while finding a command state has its charms. Like others, they found a mixture hard to manage, and so began with monetary union, hoping to expand gradually. Unlucky timing: world monetary crisis suddenly struck in 2008.