During World War II, Henderson helped train Army recruits. In the 1940s, Henderson also advocated for civil rights, including for interracial athletic competitions. Among the battles he fought in the 1940s was picketing the Uline Arena (originally a hockey venue and later called the "Washington Coliseum"), because the Uline would not allow African Americans and Whites to compete against each other. After hearing the AAU Golden Gloves Boxing competitions were to be held at the Uline, Henderson encouraged picketing until Eugene Meyer, publisher of the Washington Post, withdraw his support for holding the event there. Efforts by Henderson and Meyer ultimately led to the AAU allowing integrated boxing in the District of Columbia.