Not trying to argue with you, but remember, South Carolina seceeded from the United States, It was no longer part of the Union. As a free nation, South Carolina asked that all union forces be removed from South Carolina soil. Linclon refused and in an effort to press the matter, sent supplies to the troops at Fort Sumter with the message, hold out until the end. If we have a military base in Mexico, and mexico tells us to close it down and leave and all we do is re-supply it, can we not expect Mexico to militarily remove it.
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.