“That is true if you don’t count the union keeping forts in confederate states territory as an act of war.”
The States unlawfully attempting to secede were States in perpetual Union with the United States. This resulted in the obligation: “The United States shall guarantee to every State in this Union a Republican Form of Government, and shall protect each of them against Invasion; and on Application of the Legislature, or of the Executive (when the Legislature cannot be convened), against domestic Violence.”
Constitution of the United States
Article. I.
Section. 8.
The Congress shall have Power
To provide for calling forth the Militia to execute the Laws of the Union, suppress Insurrections and repel Invasions;
To exercise exclusive Legislation in all Cases whatsoever, over such District (not exceeding ten Miles square) as may, by Cession of particular States, and the Acceptance of Congress, become the Seat of the Government of the United States, and to exercise like Authority over all Places purchased by the Consent of the Legislature of the State in which the Same shall be, for the Erection of Forts, Magazines, Arsenals, dock-Yards, and other needful Buildings;—And
To make all Laws which shall be necessary and proper for carrying into Execution the foregoing Powers, and all other Powers vested by this Constitution in the Government of the United States, or in any Department or Officer thereof.
Article. IV.
Section. 3.
New States may be admitted by the Congress into this Union; but no new State shall be formed or erected within the Jurisdiction of any other State; nor any State be formed by the Junction of two or more States, or Parts of States, without the Consent of the Legislatures of the States concerned as well as of the Congress.
The Congress shall have Power to dispose of and make all needful Rules and Regulations respecting the Territory or other Property belonging to the United States; and nothing in this Constitution shall be so construed as to Prejudice any Claims of the United States, or of any particular State.
Section. 4.
The United States shall guarantee to every State in this Union a Republican Form of Government, and shall protect each of them against Invasion; and on Application of the Legislature, or of the Executive (when the Legislature cannot be convened), against domestic Violence.
I don’t think there was anything unlawful about it. Where is that perpetual union you keep bringing up mentioned in the US Constitution? I can’t find it in the constitution I am reading, maybe my copy is defective. States do not “belong” to the US. The federal government is currently failing miserably on the “shall protect each of them against Invasion” thing, don’t you think?