In 1776, Britain had no legal means to "secede" because their law required perpetual allegiance to the King. It was not possible to throw off British Subject status.
Therefore the word "secession" cannot apply. Only the word "Rebel" fits to describe the leaving of a nation that has no law which allows it.
The US however, adopted as it's foundation premise, that people *DO* have a right to throw off American citizenship en masse, and establish a government of their own that suits them.
This means that "secession" became legal since 1776.
Just as the word "subject" applied prior to 1776, so too did the word "Rebel" apply prior to 1776.
Since the adoption of the word "citizen" applied after 1776, so too did the word "secession" apply after 1776.
I hope this clarifies things for you.
No, in 1776 the founders used the natural right of revolution to throw off the English government after a long string of abuses and usurpations. Never expecting or believing the English would just let them go.
The foundational premise of the revolution was “ We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the pursuit of Happiness.”
The foundational premise was NOT that any people anytime for any reason can just change their government. If fact they warned against it- “Prudence, indeed, will dictate that Governments long established should not be changed for light and transient causes;”
Then they explained when the right of revolution should be used- “But when a long train of abuses and usurpations, pursuing invariably the same Object evinces a design to reduce them under absolute Despotism, it is their right, it is their duty, to throw off such Government,”
And they gave us their example- 11 years of enduring increasing despotic measures, in a system of government they had no voice in, by England all the while sending representatives to the King and Parliament to recognize their right as Englishman.
What they did not do, what they would have laughed at, was a rebellion by a group of people because a party they disagreed with won an election in a constitutional republic with a system of check and balances.