This essay suggests a hypothesis in three topics. A Watershed Event in Three Threads explains that members of the White endogamous group suffered a wave of panic, fueled by sensationalist newspapers, that Blacks were secretly plotting to massacre Whites. African-American Ethnic Solidarity Benefited suggests that the one-drop rule was reinforced and encouraged by ethnic leaders seeking to strengthen group loyalties by strengthening group boundaries. Other Voices presents four objections to the hypothesis: The hypothesis suggests that Blacks and Whites cooperated in creating the one-drop rule. It denies that the one-drop rule increased slave assets held by planters. It ignores pre-1830 literature mentioning an indelible mark. It denies that Latin America has passing literature.