Main impact of the constitution?
It shifted the balance of power from the individual states to the federal government.
That would be the amendment repealing prohibition. The 18th amendment established prohibition, and the 21st repealed it. However, to say that these amendments had no impact on the Constitution is not correct. The 18th amendment became part of the Constitution as truly as any other part, and the 21st did also. This had a major impact on the Constitution, and on the people as well.