American abolitionists’ long crusade to end slavery stands out as one of the nation’s most inspiring social movements. However, the abolitionist movement never spoke with a single, unified voice. In fact, some of the movement’s most significant impediments were its own internal divisions. In 1844 newspaper editor Jonathan B. Turner wrote in the Illinois Statesman that “there has already arisen so many various [abolitionist] sects . . . that the term ‘abolition’ like the term ‘orthodox’ really means nothing more than that a man may believe ‘some things as well as others,’ provided he sticks hard to the name.” Abolitionists had many different ideas about how to achieve abolition and how the slaves, once they were freed, should be treated.

One of the main divisions was between those who favored gradual emancipation and those...