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.