What economic effect did southern slavery have on the north? a. it was minimal, which explains why northerners opposed slavery. b. many northerners profited from investing in real estate partnerships that controlled southern plantations. c. a few new york shipping companies benefited from slavery, but the institution had little effect otherwise. d. southern slavery finance industrialization and internal improvements in the north. e. southern slavery drained resources from the north and keep the whole nation in a depression during the 1850s?