Final answer:
The U.S. Constitution was altered through a Constitutional amendment to grant 18-year-olds the right to vote.
Step-by-step explanation:
The change described in the statement is related to the granting of the right to vote to 18-year-olds who were fighting in the Vietnam War. This change came about through a Constitutional amendment. Specifically, the Twenty-Sixth Amendment to the U.S. Constitution, ratified in 1971, lowered the voting age from 21 to 18.
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