How did the voting rights act of 1965 stop discrimination in areas where voter eligibility tests were previously used?

It required federal supervision.  Many Africans were prevented from voting because they were being harassed.  To ensure that they too are able to vote, the Federal government instructed law enforcement and the National Guard to help African Americans to register and vote without fear of being driven of the voting stations.
 

Indigenous peoples were introduced to horses and the wheel, while europeans learned of many previously unknown plants.