Complex sentence: Thomas Walker (AKA "Beau Walker") came from Bristol, one of Britain's principal slaving ports; and after making his fortune in the slave trade, he immigrated to the U.S. through New York in 1792.
Split into simpler sentences: Thomas Walker (AKA "Beau Walker") came from Bristol, one of Britain's principal slaving ports. After making his fortune in the slave trade, he immigrated to the U.S. through New York in 1792.