What does the Fifteenth Amendment prevent states from doing?

Answer: The 15th amendment prevents the government from not allowing one to vote because of race, gender, age etc. (in other words prevents discrimination and gives everyone voting rights)

The Fifteenth Amendment (Amendment XV) to the United States Constitution prohibits the federal government and each state from denying a citizen the right to vote based on that citizen's "race, color, or previous condition of servitude".