Final answer:
The 21st Amendment was the first time a Constitutional Amendment was repealed, specifically repealing Prohibition in the United States.
Step-by-step explanation:
The 21st Amendment is significant because it was the first time a Constitutional Amendment was repealed. It repealed the 18th Amendment, which had established Prohibition in the United States. This marked a shift in public opinion and recognized the failure of Prohibition. The 21st Amendment returned the power to regulate alcohol to the states.
Learn more about the significance of the 21st Amendment in US history