No government could come together with the proviso that anyone and anytime could leave!
Even the Confederates could not survive that.
It would not be a compact of states but a coaliton of sovereign nations, more like the EU.
Quite correct!
It is sometimes forgotten that by July 1776, the united American colonies had been at war with the United Kingdom for over one year (if you date the onset of the war for independence to begin with the battles of Lexington and Concord in April 1775). Within a few days (July 12) of the proclamation of the Declaration, John Dickinson had submitted his draft for what was to become the Articles of Confederation and Perpetual Union.
http://www.yale.edu/lawweb/avalon/contcong/07-12-76.htm
Even then, the concept of a permanent Union of the former colonies was well established. Even then, the individual colonies/states were denied the full scope of sovereign powers, in favor of the nation.
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