What inventions did tesla contribute to?

What was one reason that southern states passed laws after 1800 to discourage manumission? 1)southern whites feared that freed blacks would seek revenge for past treatment as slaves. 2) northern leaders pressured southerners to liberate enslaved people. 3)southern states needed an inexpensive labor force to work in southern factories. 4)northern whites had sold their slaves to southerners before slavery was banned in the north.