Overlooking for a moment the fact that from the viewpoint of the administration Sumter was a U.S. fort in a U.S. city in a U.S. state, neither South Carolina or any other state holds title over federal property. Sumter was built on property deeded to the United States free and clear by an act of the South Carolina legislature. By transferring ownership the South Carolina government gave up all control over the property because Constitutionally on Congress can exercise authority over federal facilities. And that includes disposing of them.
Are you sure that South Carolina was not justified in trying to reclaim land that it already owned?
I can't speak for the people of South Carolina and what they saw as justification. I can only say that South Carolina had no legal claim to Sumter, and their act of firing on it was an act of armed rebellion against the central government. And they paid the price for their decision.
By that logic, because Virginia ceded Alexandria to the Federal District, the Federal government still holds title to the entirety of that city. Yet, that's not the case. (Yes, I know, the Federal government sold Alexandria back to Virginia due to multiple reasons, so of course it's not as cut and dry as I describe it.) According to the Northwest Ordinance, the original colonies are granted exclusive title to the land within their borders, in exchange for their cession of claims against western land, and their transfer of primary jurisdiction of said western lands to the Confederacy, followed by the reorganized Federal government.
Under common law at the time, when you hold original title to the land, and you no longer recognize the authority of the Federal government to sit on that land, the title to that land would indeed transfer back to the state.
Ironically, it would appear that according to the Northwest Ordinance, no state created from these original Western lands [Ohio, Indiana, Illinois, Michigan, Wisconsin, and Minnesota] have any right of secession, as Congress (a) declares that the Western lands are forever to remain in the Confederacy of the United States, and (b) that Congress shall hold primary disposal of Western lands.
Art. 4. The said territory, and the States which may be formed therein, shall forever remain a part of this Confederacy of the United States of America, subject to the Articles of Confederation, and to such alterations therein as shall be constitutionally made; and to all the acts and ordinances of the United States in Congress assembled, conformable thereto. The inhabitants and settlers...The legislatures of those districts or new States, shall never interfere with the primary disposal of the soil by the United States in Congress assembled, nor with any regulations Congress may find necessary for securing the title in such soil to the bona fide purchasers.
(I'm looking at finding the reference where the original colonies were granted full title to land within their borders, but it doesn't seem to be in here. Perhaps I am thinking of another Act, which I'll promptly go and find!)
On another side of the issue, is it appropriate for the Federal government to turn the guns of the forts, which were built to defend South Carolina from foreign invaders, inland towards Charleston?
I can't speak for the people of South Carolina and what they saw as justification. I can only say that South Carolina had no legal claim to Sumter, and their act of firing on it was an act of armed rebellion against the central government. And they paid the price for their decision.
How was it an act of armed rebellion against the central government, if the State government no longer recognized the authority of the central government? Under the American Federal system, the authority of government orginally began at the local/individual level, and via grants made first to the State government, and then via grants from the State to the Federal government*. And seeing how (a), South Carolina was not threatening to invade the District of Columbia, and (b) there were no threats to the other States in the nation by the independence of South Carolina, where was the rebellion?
(* Of course, with the changes made to our government beyond the end of the Civil War, this is no longer the case. The Federal Government has proven to us that it is our Sovereign, and that we should serve it with our entire servitude.)