>The constitution did not give states the right to secede.

the right to secede is, unfortunately, given or taken by force only. As US Revolution and Civil War, or Kosovo or Crimea among others show.

No. Montenegro seceded peacefully from Serbia. Czechoslovakia dissolved into two parts peacefully (no seceding, but close enough). Finland seceded peacefully from Russia. Amongst others...

And then, of course, there's the former Soviet Union...

Most African decolonisation was also peaceful.

India's decolonization was also mostly peaceful. What was not peaceful in India was the post-independence separation between Pakistan and India.

pretty much all of these cases were "crumbling/dissolution of empire" or similar. I.e. an opportunity presented by dramatic shift in force balance when dominating force is weakened and thus couldn't stop the process. It wasn't a result of a process legitimate according to the laws at that moment in that geography. And that is exactly my point (it wasn't about peacefulness - if you have obviously prevailing force, the things have good chances to happen peacefully, like in case of Crimea :). It is always about force. Laws, like always, follow the force and legitimaze the separation after the fact.

Well the American States were BORN from the right to secede from the English Crown, and they clearly kept that Right in their constitution before of their very History on that matter.

In the eyes of the colonists the separation happened in London, not in the colonies. The fighting started because they wanted "their rights as Englishmen" and nothing more.

There's a reason the Declaration of Independence happened more than a year after the first spurts of military action (and was very controversial in the colonies even then).

This comment would have been stronger without the second sentence.