Gadsden had supported nullification in 1831, and he advocated secession by South Carolina in 1850 when California was admitted to the Union as a free state. Gadsden considered slavery “a social blessing” and abolitionists as “the greatest curse of the nation.” When that secession failed, Gadsden, working with his cousin Isaac Edward Holmes, who had moved to San Francisco in 1851 to practice law, and the California state senator Thomas Jeffe...