Which best explains why many African Americans had not registered to vote by the 1960s?

The correct answer is intimidated by violent threats and actions.

During the 1960's, African-Americans still faced a significant amount of discrimination in American society. This included threats and physical violence. Groups like the Ku Klux Klan, a white supremacist organization, used fear tactics in order to stop African-Americans from voting during this era. This included death threats or actually violence if they showed up to the polling place.