The Declaration of Independence is a secession document. The “thirteen united States of America” seceded from the British Empire and became “Free and Independent States” like the “State of Great Britain.”And then . . .
The Constitution for the United States—the same Union of sovereign States that existed under the Articles of Confederation—allowed the States to secede from the Articles by acceding to the new governing document. This was expressly prohibited by the Articles.
The Hartford Convention of 1815 urged Northern states to nullify laws in support of the War of 1812 (several had already done so in fact but not by legislation) and insisted that if nothing changed they would have to resort to secession. Daniel Webster, the same man who called nullification disunion in 1830, believed in it enough in 1812 that he made several speeches in support of the idea around his home district.More here.