Final answer:
The enactment of the 26th Amendment expanded suffrage by lowering the voting age from 21 to 18 during the Vietnam War.
Step-by-step explanation:
The enactment of the 26th Amendment to the Constitution advanced the cause of suffrage by lowering the voting age from 21 to 18. This amendment was passed in 1971 during the Vietnam War, and it gave young men who were fighting in the war the right to vote for or against decisions that directly affected their lives. By reducing the voting age, the amendment expanded the rights of young people and increased their representation in the democratic process.