Final answer:
Henry Adams left Shreveport for New Orleans in 1878 due to a government subpoena and the threat of harm from White supremacist groups, continuing his work on African American emigration and rights.
Step-by-step explanation:
When Henry Adams left Shreveport, he was fleeing due to a government subpoena requiring him to testify to Congress about Black voter suppression in Louisiana. Given the high tension and the presence of White supremacist groups, his return to Louisiana could have resulted in personal harm.
Instead, Adams moved to New Orleans in 1878 and continued to work on advocacy for African American emigration and rights, collaborating with groups like the Colonization Council and the American Colonization Society, and for a time supporting the Black southern migration to Kansas.