Note: the federal government INVADED the southern states . . . the southern states DID NOT INVADE the states in "the union" . . . based upon the opinion of the Supreme Court of the United States . . . the Confederate States of America had every right to defend themselves against the invasion

the sovereign States of Arizona and New Mexico have "declared" an INVASION by a foreign nation --- under the Constitution, the President and Congress is bound to repel it . . .
The Prize Cases, 1863
The United States Supreme Court


Opinion: Mr. Justice GRIER.

By the Constitution, Congress alone has the power to declare a national or foreign war. It cannot declare war against a State, or any number of States, by virtue of any clause in the Constitution. The Constitution confers on the President the whole Executive power. He is bound to take care that the laws be faithfully executed. He is Commander-in-Chief of the Army and Navy of the United States, and of the militia of the several States when called into the actual service of the United States. He has no power to initiate or declare a war either against a foreign nation or a domestic State. But by the Acts of Congress of February 28th, 1795, and 3rd of March, 1807, he is authorized to call out the militia and use the military and naval forces of the United States in case of invasion by foreign nations, and to suppress insurrection against the government of a State or of the United States.

If a war be made by invasion of a foreign nation, the President is not only authorized but bound to resist force by force. He does not initiate the war, but is bound to accept the challenge without waiting for any special legislative authority. And whether the hostile party be a foreign invader, or States organized in rebellion, it is none the less a war, although the declaration of it be "unilateral."…

The greatest of civil wars was not gradually developed by popular commotion, tumultuous assemblies, or local unorganized insurrection. However, long may have been its previous conception, it nevertheless sprung forth suddenly from the parent brain, a Minerva in the full panoply of war. The president was bound to meet it in the shape it presented itself, without waiting for Congress to baptize it with a name, and no name given to it by him or them could change the fact.

It is not the less a civil war, with belligerent parties in hostile array, because it be called an "insurrection" by one side, and the insurgents be considered as rebels or traitors. It is not necessary that the independence of the revolted province or State be acknowledged in order to constitute it a party belligerent in a war according to the law of nations. Foreign nations acknowledge it as war by a declaration of neutrality. The condition of neutrality cannot exist unless be two belligerent parties…

Whether the President in fulfilling his duties, as Commander-in-Chief, in suppressing an insurrection, has met with such armed hostile resistance, and a civil war of such alarming proportions as will compel him to accord to them the character of belligerents, is a question to be decided by him, and this Court must be governed by the decisions and acts of the political department of the Government to which this power was entrusted. "He must determine what degree of force the crisis demands." The proclamation of blockade is itself official and conclusive evidence to the Court that a state of war existed which demanded and authorized a recourse to such a measure, under the circumstances peculiar to the case…

If it were necessary to the technical existence of a war, that it should have a legislative sanction, we find it in almost every act passed at their extraordinary session of the Legislature of 1861, which was wholly employed in enacting laws to enable the Government to prosecute the war with vigor and efficiency. And finally, we find Congress…passing an act "approving legalizing, and making valid all the acts, proclamations, and orders of the President, etc., as if they had been issued and done under the previous express authority and direction of the Congress of the United States"…

…we are of the opinion that the President had a right, jure belli, to institute a blockade of ports in possession of the States in rebellion, which neutrals are bound to regard.