Why would white southerners pass laws that controlled the movement of african americans? what would happen if african americans left the south in huge numbers?

They would have lost there political advantage numbers

Ithink the answer is b.)

The  pan-african movement  was an "emotional, cultural, psychological and ideological  movement  that began among the  african  dispora in the western hemisphere, for a closer  purpose, so that  african  people could feel secure, attain political, economic as well as psychological power visa vis other races or world regions" .