What was the most important social event from 1848-1877?

What directive in source a might have been at the root of the action described in source b?

Brainliestttme : ) what caused the first opium war? chinese confiscation and destruction of british opium chinese support for the boxer rebellion british efforts to increase opium prices british attempts to force china to accept opium as payment

Which would make the best heading for this list of notes about the migration of african-americans during the reconstruction era?