Actually Buchanan sent a message to congress in Dec of 1860 stating that he believed Secession was illegal, but also that the federal government had no right to force states to remain in the Union. Once again showing what a spineless bastard he was and cementing him as the worse president in our nations history.
Can someone show me in the US Const. where secession both defined and is made unconstitutional?
And therein lies the rub. Could Lincoln have negotiated the Southern states back into the Union? Quite possibly, but we will never know, because he chose a deliberately provocative act.
On what basis? That the Constitution didn't specifically allow for it? Well English Law didn't allow for secession either, but our people articulated the belief that the laws of nature, and of nature's God allows for it, and therefore it was legal.
I don't know why we would argue natural law for our own independence, and deny natural law for other people's independence. That doesn't even make sense. It is hypocritical.