and South Carolina wasn't provoking anyone by surrounding 50 US troops with thousands of armed men?
I believe the big buildup in Confederate and state troops around the harbor occurred when it became known that an armed force was coming south. From The Memphis Daily Appeal of April 7, 1861, quoting special dispatches to the New Orleans Delta:
GREAT EXCITEMENT IN CHARLESTON, S.C.
Washington, April 3. -- A special messenger from the officer commanding on Morris Island, arrived at Charleston to-day, bringing intelligence of a suspected attempt to reinforce Fort Sumter, or at least to throw a supply of provisions into the place. ...
From another article in that same issue of the Daily Appeal:
Special Dispatch to the Constitutionalist
Charleston, April 4. -- There is an unusual military preparation going on here. The soldiers and officers have been ordered to their posts. I presume that something unusual is going to happen ere long.