.American and European Unions, Compared(1)
The (1648) Treaty of Westphalia created the modern nation-state by respecting sovereignty within agreed boundaries. Soon, everyone had a sovereign King. Today, Europeans live in republics, but wish to unite for economic benefits. Like others however, they found that hard to do, and so began with monetary union, alone. Unlucky timing: world monetary crisis suddenly struck.
Although the nations of the world are still a long way from agreement on a United Nations or any other set of supranational rules, a surprising amount of consensus has evolved over the centuries. Using the example of the axioms underlying Euclid's geometry, a few basic assumptions have to be made, which cannot be proven; change one of those axioms, and the whole structure of governance changes.
Boundaries of the state. A group of some sort may form a close association, but unless it stays within stated boundaries, it is a Tribe. At the Treaty of Westphalia in 1648, most of the European tribes agreed to stated boundaries, and those boundaries define nations. Unfortunately, former residents of the bounded area may dispute the ownership. Even when there are no known descendants of former residents, the title of current residents ultimately rests on tradition and the threat of force.
Citizenship. Somewhat greater variation is seen in the definition of a citizen, but most nations confer citizenship to children of citizens, to those who were born within the nation's boundaries, and to still others as defined by the rulers of the nation.
Ownership of real estate.
How is the ruler chosen>
Who makes the day to day rules, who enforces them?