I'm unsure why you think this was erroneous, as Congress most surely shares this power with the executive. Unless you think the President is empowered by the Constitution to make war and peace at his own pleasure?
BTW, in his speech denying the right to secede, Buchanan refers to seditious pamphlets spread by abolitionists throughout the South in 1835. Let's leave aside this was 25 years before. Do you know of anywhere the text of such pamphlets is available? I'm curious to read them.
It's not a shared power.
The authority to declare war belongs to the legislative branch via Article 1, Section 8, Clause 11.
The ability to make peace belongs to the executive branch via Article 2, Section 2, Clause 2.
IMHO, the Founders rightly believed it should be difficult to start war, yet easy to end it.
§ 1168. In the convention, in the first draft of the constitution, the power was given merely "to make war." It was subsequently, and not without some struggle, altered to its present form. It was proposed to add the power "to make peace;" but this was unanimously rejected; upon the plain ground, that it more properly belonged to the treaty-making power. The experience of congress, under the confederation, of the difficulties, attendant upon vesting the treaty-making power in a large legislative body, was too deeply felt to justify the hazard of another experiment.
Joseph Story Commentaries on the Constitution
Let's leave aside this was 25 years before. Do you know of anywhere the text of such pamphlets is available? I'm curious to read them.
No, but doing a general search for the year and the subject usually brings up something.