Which of course has nothing at all to do with whether secession is legitimate, America having been born in secession from the British Empire, or whether London held the moral high ground because they proclaimed emancipation for the slaves.
Not to mention that the author of the Declaration was himself an owner of slaves, which is conveniently ignored by those seeking to use the document as addressing slavery.
The fact is that, the South had no moral right to revolt and there is no legal basis for secession.