What event officially began the Civil War?

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

Ascientist performs an experiment where she measures the mass of a piece of metal, pours acid onto the metal, washes the metal, and then re-measures the mass of the metal. the scientist repeats the experiment several times, each time increasing the amount of acid used. the dependent variable in the experiment is the: initial mass of the metal final mass of the metal amount of acid used washing the metal

Who coined the phrase “go west and grow with the country”?