"If it was legal for the US to leave the British Empire when they wished to, why was it illegal for the South to leave the US when THEY wished to? The only difference that I can see is that the South lost the Civil War, but the US won the Revolution (or maybe the BE had too many other wars going to spend the money and time to win it). But if that's the only difference, then law is simply a matter of superior force. In which case, each of us needs as many guns and as much ammunition as he or she can assemble."

Precisely! ;-D It's always a matter of superior force, and who holds the field of battle at the end of the campaign. The victors make the rules and the victors decide what's "right", "just", and allowable. And thus it always has been throughout history.

This is why despots, hypocrites, scoundrels, and heartless imperialists often get to parade around grandly before their own public and present (and even imagine) themselves as champions of freedom.