[jeffersondem]

“So even if we agree (and I don’t) that states can just proclaim themselves independent countries at will, then actions taken before they made this claim are treason.”

The colonists may have fired the first shot in the First War for Independence. So what if they did? It does not invalidate the actions of the Free and Independent States (even though 13 of those states were slave states).

[BroJoeK]

jeffersondem: "The colonists may have fired the first shot in the First War for Independence.
So what if they did?
It does not invalidate the actions of the Free and Independent States (even though 13 of those states were slave states)."

It depends on how you define "first shot".
At the Boston Massacre Brits were the only ones who fired, into a crowd.
At Lexington it's not known who fired first, but the casualties were one Brit and eight Americans.
More important, British Army presence in Lexington to confiscate American arms was itself an act of war, even without any shooting.

And it was only the latest in a long series of "Intolerable Acts" against Americans, including abrogating the 1691 Massachusetts Charter of self government.
So, in the 1770s Brits acted against Americans and Americans reacted to that "long train of abuses and usurpations".
In the 1860s Confederates acted against Americans, including abrogating the 1788 US Constitution, and so Americans reacted to Confederate aggressions, injury and oppressions...

By the time of the 1776 Declaration of Independence Americans had already fought over two dozen named battles against the Brits.
Nothing remotely similar existed in November 1860.