Constitution Series Part 25: Article IV, Sections 3 and 4

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.

Constitution Series Part 24: Article IV, Sections 1 and 2

With the major stuff out of the way, only a few details remain before we can put a pin in this document that details what constitutes our government. The biggest detail (and, therefore, the biggest article of what remains) is about the relationship between the states and the federal government, and the relationship between the states and themselves.

As a reminder, when I quote the Constitution in these posts I'm quoting from the transcript of the Constitution at the Federal Archives website.

Constitution Series Part 14: Article I, Section 10

Article I of the United States Constitution is ostensibly about Congress, but in fact it touches on every branch of the government, as well as governments below the national level. It's due to this scope and laying down the foundations of what's to be expected of our government as a whole that Article I takes up approximately 50% of the entire Constitution. The rest just kind of builds upon the groundwork laid by Article I.

Section 10 in particular focuses on limitations placed upon the states. Some are absolute limitations, while others require Congressional approval to circumvent. I assume it's these Congressional consent clauses that make these limitations appropriate for Article I.