The regulatory history of voting in the United States is complex to say the least. Roughly 20 acts, including constitutional amendments, have changed who is eligible to vote since 1789. Originally it was up to the states to decide – which generally limited voting rights to white property owning, or tax paying, men. This disenfranchised a number of people groups as only about 6% of the population met those requirements at the time.
Since then we have continued to open up voting to all people-groups in order to treat it as an individual right. One caveat to this may be those convicted of a felony, whom society has deemed unfit to vote (which has developed its own controversy) – another caveat would be persons under the age of 18 whom society has not labeled as adults. Recently this too has become controversial.