The letter the rebel representatives presented to the state department leaves no room for negotiation. They proclaim that the "confederacy" is a separate nation...period.
"In that communication Messrs. Forsyth and Crawford inform the secretary of State that they have been duly accredited by the Government of the Confederate States of America as commissioners to the Government of the United States, and they set forth the objects of their attendance at Washington. They observe that seven States of the American Union, in the exercise of a right inherent in every free people, have withdrawn, through conventions of their people, from the United States, reassumed the attributes of sovereign power, and formed a government of their own, and that those Confederate States now constitute an independent nation, de facto and de jure and possess a government perfect in all its parts, and fully endowed with all the means of self-support.'
Seward's response to them is exactly what Lincoln said during his inaugural.
"The Secretary of State frankly confesses that he understands the events which have recently occurred, and the condition of political affairs which actually exists in the part of the Union to which his attention has thus been directed, very differently from the aspect in which they are presented by Messrs Forsyth and crawford. He sees in them, not a rightful and accomplished revolution and an independent nation, with an established government, but rather a perversion of a temporary and partisan excitement to the inconsiderate purposes of an unjustifiable and unconstitutional aggression upon the rights and the authority vested in the Federal Government, and hitherto benignly exercised, as from their very nature they always must so be exercised, for the maintenance of the Union, the preservation of liberty, and the security, peace, welfare, happiness, and aggrandizement of the American people. The Secretary of State, therefore, avows to Messrs. Forsyth and Crawford that he looks patiently, but confidently, for the cure of evils which have resulted from proceedings so unnecessary, so unwise, so unusual, and so unnatural, not to irregular negotiations, having in view new and untried relations with agencies unknown to and acting in derogation of the Constitution and laws, but to regular and considerate action of the people of those States, in cooperation with their brethren in the other States, through the Congress of the United States, and such extraordinary conventions, if there shall be need thereof, as the Federal Constitution contemplates and authorizes to be assembled."
There is zero room for negotiation from those two starting points.