“Article 1 Section 10, Clause 1: No State shall enter into any Treaty, Alliance, or Confederation;
Refresh my memory, what did the sesseionists call their "Country" ?”
First, a state is a state in regards to those state within the union. Those states that have left the union are no longer covered by that clause. The clause relates to foreign entities.
“Clause 1: 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.”
Just what does that have to do with secession? That relates to dividing or joining states to form new states. That was placed in their to prevent a hostile takeover by forming states with greater powers.
“Clause 2: 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.”
Again, this covers only states belonging to the union. It does not prevent secession.
“Clause 2: 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, Even the Document linked by sheltonmac above, acknowledges the "Common territory of the Republic" placing the area of the United States under a degree of congressional control.
Clause 1: 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.”
To begin with a State is a political entity by definition, and in forming the Confederacy, the states were violating the Constitution.
Continuing, That having been said, the Fully half of the states that seceded were Created by the Union.(in the Louisiana Purchase)...
Now, If you wish to argue about the original ratifiers, that might be one thing, However, Every state West of the Mississippi had it's Freedom from France negotiated and Paid for , by the Union Government....Now I am not saying they should have remained without rights, but surely they were more securely bound to the Union than say, the Southeastern states...
Further, As the document linked above by sheltonmac clearly lays out, there was no long list of usurpations and horrors, they were losing at the table of Democracy, and didn't like it.