Corwin Amendment is a simple American decision. The Corwin Amendment was a proposed amendment to the Constitution intended to protect "domestic institutions" of the states from the federal constitutional amendment process and from abolition or interference by Congress. Although it does not explicitly mention slavery, it was designed specifically to with that in mind. The judicial implications of the decision is however not represented in the game.
The decision shows up in the tab before the American Civil War if 
USA has Slavery allowed and have a consciousness of at least 4. It is then possible to take, when USA has a consciousness of at least 7 and it lowers consciousness by 2.