In most instances resupply against a treaty stipulation is a cause for war.
On the twenty-ninth of March, Lincoln had ordered that three ships — the Pocahontas, the Pawnee, and the Harriet Lane — together with three hundred men and provisions be made ready to sail for the Charleston harbor. Lincoln to Cameron, in Official Records: Armies, Series I, Volume I, page 226; Enclosure No. 1, op. cit., page 227.
These orders were all marked private. On the first of April, he sent a message to Commandant Andrew H. Foote at Navy Yard in Brooklyn, New York to “fit out the Powhatan to go to sea at the earliest possible moment under sealed orders.”Lincoln to Andrew H. Foote, in op. cit., page 229
These instructions were confirmed with another telegram which contained these words: “You will fit out the Powhatan without delay. Lieutenant Porter will relieve Captain Mercer in command of her. She is bound on secret service; and you will under no circumstances communicate to the Navy Department the fact that she is fitting out.” In all, consisted of eight warships, carrying twenty-six guns and one thousand, four hundred men.
Fort Sumter Relief Force...On Its Way Four Warships, 25 guns, 300 (additional) seamen, 200 artillerist U.S.S. Powhatan 2415 Tons Armament*- 3 (Three 12-pounders) Carrying 300 additional seamen to assist in the resupply/reinforcement effort. (Never arrived.)Smug note; By a quirk of fate Lincoln had previously ordered the Powhatan to the aid of Ft. Pickens and it had already set sail to Florida. U.S.S. Pawnee 1289 Tons Armament*- 10 (Eight 9-inch guns, Two 12-pounders) U.S.S. Pocahontas 694 Tons Armament*- 6 (Four 32-pounders, One 10-inch rifle, One 20-pounder Parrott) U.S.S. Harriet Lane (revenue cutter) 600 Tons Armament*- 2 (Two 32-pounders) Baltic (transport) Armament- None Carrying 200 troops (artillerist) for the re-inforcement of Fort Sumter. Gunboats Thomas Freeborn 269 Tons Armament*- 2 (Two 32-pounders) (Never arrived.) Uncle Ben Captured by pro-secessionists off the coast of North Carolina. Yankee 328 Tons Armament*- 2 (Two 32-pounders) *earliest report in proximity to the time of Fort Sumter
The day this flotilla set sail the CSA received copies of these orders, and this set in motion the reduction of Sumter.
On the twenty-eighth of March the Senate asked Lincoln if he had anything of note to tell them before they adjourned. He said no. From the Congressional Globe:
Mr. Powell, from the committee appointed to wait on the President of the United States and notify him that unless he has some further communication to make, the Senate is ready to adjourn, reported that the committee had waited on the President, and been informed by him that he had no further communication to make to the Senate.
Lincoln apparently wanted the Congress out of the way before he took action that his own advisers had warned him would result in a shooting war.
It is of course inaccurate to refer to the informal and apparently verbal agreement between the Buchanan administration and South Carolina as "a treaty." Treaties require that the Senate "advise and consent."
Lincoln publicly notified South Carolina on April 06 that he would attempt to reprovision the fort, but not to bring in reinforcements or armaments unless the Fort or the expedition was attacked, which would from his point of view break the informal truce.
The CSA could have chosen to view the attempt to reprovision as maintenance of the status quo and allowed it to proceed. Or for that matter they could have reprovisioned the fort themselves, leaving a couple hundred men stranded indefinitely in a position where they could accomplish nothing militarily. This would have been a magnificent gesture of contempt.
They chose instead to launch an attack. I believe it to be fairly obvious that this decision was made to force the remainng slave states to "get off the fence." This decision may have been partially precipitated by a vote on April 04 of 80 to 45 against secession in the Virginia Convention, leading the CSA cabinet to worry that perhaps the tide of opinion was turning against them in the Upper South and that something must be done to break the stalemate.
The entire cabinet was in agreement with the decision to attack Sumter except Robert Toombs, the Secretary of State. He said, "Legions now quiet will swarm out and sting us to death. It is unnecessary. It puts us in the wrong. It is fatal." With the advantage of hindsight it is pretty obvious that his remarks were correct.
military status should remain as it was at the time of this understanding, viz., on December 9, 1860
I am unclear whether an attempt to reprovision but not to reinforce or resupply armaments is usually considered to be changing "military status." Since it creates no alteration in the balance of forces, I assume that from the generic use of the terms it would not. However, the term "military status" may have specific meanings with which I am unfamiliar.
I would also like to point out that if an alteration in the supply of provisions constitutes a change in military status, the South made that change when they cut off provisions to the fort on April 07.