On June 19, 1965, Martin Luther King Jr. gave a commencement address to Antioch College’s 296 graduates, plus some 1,200 others who crowded the outdoor gathering space by the school’s main building. He spoke of American civil-rights issues — he was only three months past the national crisis in Selma, Ala., where racist officials tried to stop a march. And there would be more struggles in the future.