Why didn’t black Americans simply vote for more rights before the era of the civil rights movement?

They almost didn't have a right to vote

Explanation:

Even though the 15th Amendment says black men should have a right to vote, the Caucasians had a hard time practicing it and the African Americans almost had no right to vote until after the civil rights movement started. In 1965, Lyndon B. Johnson signed the Voting Rights Act which was aimed to overcome legal barriers that prevented African Americans from exercising their right to vote, as promised in the 15th amendment

d) the constitution rights of native americans and their right to self-government on reservations

i also think it is c