In 1914-15, after withdrawing from the Socialist Party, Harrison began work with freethinkers, the freethought/anarchist-influenced Modern School Movement (started by the martyred Spanish anarchist/educator Francisco Ferrer), and his own Radical Forum. He also spoke widely on topics such as birth control, evolution, literature, nonbelief, and the racial aspects of World War I. His outdoor talks and free speech efforts were instrumental in developing a Harlem tradition of militant street corner oratory. He paved the way for those who followed, including A. Philip Randolph, Marcus Garvey, Richard B. Moore, and (later) Malcolm X.