It doesn't take a brain surgeon to know that the humans in the holds of slave ships were not "immigrants", they were slaves, sold into slavery by others. They were not chained in the holds of ships dreaming about coming to American because it was the land of the free. Many of these "immigrants in fact not only suffered horribly but died on the trip to America.
Dr. Ben Carson will have to apologize quickly for this one, and expect to hear him say he misspoke.