African Americans have had the right to vote, on paper at least, since the 15th Amendment to the U.S. Constitution was ratified in 1870. But several U.S. states found ways to disenfranchise black voters through obstacles such as poll taxes and literacy tests. Harassment and threats to keep voters away from the polling places were common in some places.

It wasn’t until the 1965 Voting Rights Act that black voters were finally allowed to exercise their democratic rights.

Martin Luther King Jr. helped to lead the grass-roots struggle to enforce black voting rights. He brought the struggle to national attention with the 1965 Selma to Montgomery marches in Alabama, which peacefully but defiantly showed blacks’ determination to vote despite segregation and racist state laws.

President Obama honored the Selma marchers 50 years later on March 7, 2015. “Fifty years ago, registering to vote here in Selma and much of the South meant guessing the number of jellybeans in a jar, the number of bubbles on a bar of soap. It meant risking your dignity and, sometimes, your life,” he said.

President Obama, left, votes early for the midterm election at the Dr. Martin Luther King Community Service Center on October 20, 2014, in Chicago. (© AP Images)

Obama called the Voting Rights Act “one of the crowning achievements of our democracy.” He said the history of racial relations in the United States “still casts its long shadow upon us,” but equal rights for minorities, as well as for women and LGBTI individuals, have greatly advanced over the past 50 years.

“To deny this progress, this hard-won progress — our progress — would be to rob us of our own agency, our own capacity, our responsibility to do what we can to make America better,” Obama said.