'a document about the future of slavery in all territory acquired from Mexico'.
Becasue the Wilmot Proviso put forward a law to ban slavery in states that had been taken over by Mexico in the Mexican War.
After Napoleon's domination of Europe from around 1800 to 1814, the rulers of Europe wanted to insure that no one would ever be able to come so close to taking over all of Europe again. To this end, the diplomats from all of the Great Powers met at the Congress of Vienna to negotiate from 1814 to 1815. There they reorganized European boundaries in hopes of creating a stable Europe where coalitions of nations could always ally to defeat one nation that got out of hand.
