This treaty established the domination of the United States in the West, effectively removing Mexico as a deterrent to continental rule. The treaty allowed for the US to continue expanding states, and would also lead to more sectional tension between the North and South as the debate over slave territory would continue with the addition of these new territories.
This amendment changed the country's stance on slavery, effectively ending it forever. The Civil War was undoubtedly about the issue of slavery, and after the Southern Confederacy was forced to rejoin the Union after losing the war, the slavery issue was resolved. The passing of this amendment signified the security and political dominance that the Northern abolitionists had after the war.