Assuming for a moment that the South Carolina secession was actually legal to begin with, they had no claim to Sumter. It was in all respects the property of the United States government. The very act of demanding it be turned over could be seen as an act of war, never mind surrounding it with artillery and shooting at anything flying the Stars and Stripes that came near.
They were negotiating for rights to Sumter, Moultrie, and other arsenals. Buchannen agreed to not reinforce the forts until a decsion was made. Unfortunately, the commanders disregarded this agreement, raided the arsenal, abandoned Moultrie, and prepared for conflict at Sumter. Lincoln would not even address the SC envoys in early 1861 and further ignited the war by provisioning Sumpter.
According to you the South was supposed to ask for permission to leave the Union first?! Now that is stupid! Its like saying that the Founders were supposed to ask permission from King George and Parliament to leave the crown and become independent for it to be legal. You missed the "Liberty" boat, and are standing at the dock with your ticket in hand wondering what happened.
For something to be a right, it means that you don't have to ask permission from anybody for it. It is something that exists and that you avail yourself of.
Let us assume for a moment that any sovereign State that voluntarily joined the union can voluntarily withdraw. In that case, Lincoln's aggressive actions with respect to Sumter were "illegal".
From this point of view, Lincoln and other politicians from the northern States recognized an opportunity to gain control over the resources in the southern States. Clearly, the war that followed was one of conquest by wealthy business interests in the north and their politicians.
Kinda like Guantanamo, eh?
It seems as though you either skipped school while American History was taught, or you attended a government school.
The individual states had a Constitutional right to secession from the Union of the States. Lincoln did not want the North to lose revenues from the ridiculously high taxes being levied upon the southern states, nor did he want to lose face in his war to federalize the nation.
Additionally, the Emancipation Proclamation wasn't worth the paper it was written on. It addressed only the southern states, which, by their Constitutional right, had already seceeded (He had no jurisdiction). It applied no directive to any of the northern states, although slavery was quite common there, as well.
Lincoln was not particularly fond of blacks. He said so. He even said in two separate speeches that the issue of slavery was not an issue to him, even stating the he believed that the white race was superior! (I personally believe we're all equal)
The Constitution gave a specific few rights to the federal government (I think the number was 17). Those not specifically assigned to the fed went to the individual states. Lincoln tried to change that and the South rebelled. The South was right.
The War of Northern Agression was just that. The war was about States rights vs. a centralized federal government (which we have today). Unfortunately, history is written by the winners. Lincoln was a war criminal for invasion of a sovereign land and the massacre of its people. I believe Thomas Jefferson would have shot Lincoln for what he did to our country.