As the debate over slavery and abolition ratcheted up in the 1840s and 1850s, both the New School and the Old School began to experience internal tensions, largely along North-South (abolitionism vs. pro-slavery) lines. As the ABCFM and AHMS refused to take positions on slavery, some Presbyterian churches joined the abolitionist American Missionary Association instead, and even became Congregationalists or Free Presbyterians. African-American Presbyterian pastor Theodore S. Wright helped to form anti-slavery societies, such as the American Anti-Slavery Society and the American and Foreign Anti-Slavery Society. New School Presbyterian Rev. Henry Ward Beecher, advocated for rifles ("Beecher's Bibles") to be sent through the New England Emigrant Aid Company to address the pro-slavery violence in Kansas. While Harriet Beecher Stowe's Uncle Tom's Cabin made the case against slavery, her husband continued to teach at Andover Theological Seminary.