The amendment is the only constitutional amendment that was ratified by approval of conventions in three fourths of the state

The Twenty-first

Explanation:

The twenty-first amendment has been added to the Constitution of the United States as the repeal of the Eighth amendment.

The Eighth amendment from 1919. called to the nationwide prohibition of alcohol, it's manufacturing, trade, and consumption. The twenty-first amendment from 1933. repealed this prohibition and, as such, it is the only amendment to repeal another one.

The uniqueness of this amendment also is the fact that it is the only amendment that was ratified by state ratifying conventions, and not by legislatures of the states.

b: to eliminate competition from other farmers