By what process were eighteen-year-olds fully granted the right to vote?

The process by which eighteen-year-olds were fully granted the right to vote was a constitutional amendment, specifically the 26th Amendment to the United States Constitution. Ratified on July 1, 1971, this amendment lowered the voting age from 21 to 18 years. The amendment process is significant because it involves a formal change to the Constitution, which is a rigorous procedure requiring either two-thirds of both houses of Congress to propose an amendment or a national convention called by two-thirds of state legislatures. Following this, three-fourths of state legislatures must ratify the amendment for it to become part of the Constitution.

This constitutional change was emblematic of the larger social movements of the 1960s and early 1970s, which argued that if individuals were old enough to be drafted into military service, they should also be allowed to vote. The 26th Amendment reflects the recognition of the rights of younger citizens and ensures their voices in the democratic process, reinforcing the principle of inclusivity in American elections.