The Fifteenth Amendment to the Constitution, one of three ratified after the American Civil War to grant freedmen full rights of citizenship, prevented any state from denying the right to vote to any citizen based on race. This was primarily related to protecting the franchise of freedmen, but it also applied to non-white minorities, such as Mexican Americans in Texas . The state governments under Reconstruction adopted new state constitutions or amendments designed to protect the ability of freedmen to vote. The white resistance to black suffrage after the war regularly erupted into violence as white groups tried to protect their power. Particularly in the South , in the aftermath of the Civil War whites made efforts to suppress freedmen 's voting. In the 1860s, secret vigilante groups such as the Ku Klux Klan (KKK) used violence and intimidation to keep freedmen in a controlled role and reestablish white supremacy. But, black freedmen registered and voted in high numbers, and many were elected to local offices through the 1880s.
Eighteen is the most common voting age, with a small minority of countries differing from this rule. Those with a national minimum age of 17 include East Timor, Greece, Indonesia, North Korea, South Sudan and Sudan. The minimum age is 16 in Argentina, Austria, Brazil, Cuba, Ecuador, Nicaragua and the Isle of Man , Jersey and Guernsey (three self-governing British Crown Dependencies). People aged 16–18 can vote in Bosnia, Serbia and Montenegro if employed. The highest minimum voting age is 21 in several nations. Some countries have variable provision for the minimum voting age, whereby a lower age is set for eligibility to vote in state, regional or municipal elections.