[DoodleDawg]

At the time of the Ft. Sumter incident the fort wasn't even in the United States.

Assuming for the sake of argument that was true, so what? How does that change ownership?

Secession changes things.

In what way?

That is why the British no longer have garrisons at their previous Fort Augusta...

Ownership settled by the Treaty of Paris in 1783.

...Fort Barrancas...

Purchased along with the rest of Florida in 1821.

...Fort George, Fort Mackinac, Forte Bute, Fort Prince George, Fort William and Mary, and so forth and so on.

Again, ownership settled by the Treaty of Paris in 1783.

What transferred ownership of Fort Sumter?

[DiogenesLamp]

Ownership settled by the Declaration of Independence. Stop trying to have one standard for the 13 slave owning states, and a different standard for the 11 slave owning states.

[jeffersondem]

“Ownership settled by the Treaty of Paris in 1783.”

The American secession occurred in 1765. That was before 1783.

King Georg's War started to wind down with Cornwallis’ surrender in 1781 followed by the British withdrawal from Charleston and Savannah in 1782.

As noted, the negotiated Treaty of Paris occurred in 1783.

Now, ask me how that relates to the price of property suitable for maintaining forts.