The correct number 4) allow former male slaves the right to vote.
The Fifteenth Amendment to the United States Constitution was primarily meant to allow former male slaves the right to vote.
The 15th Amendment to the United States Constitution was ratified on February 3, 1870. This Amendment was so important because it prohibits the states or the federal government to deny the right to vote to any citizen of the US based on its race or the fact that it was a slave in the past. This amendment was applauded by the people in the North, but it was not well received in the southern states.