Why Did Slavery Become More Central to American Politics in the 1840s

Why did slavery become more central to American politics in the 1840s?

A) The Methodist Church, the nation's largest denomination, called on all its members to free their slaves.
B) Territorial expansion raised the question of whether new lands should be free or slave.
C) Members of the abolitionist Republican Party, formed in 1844, insisted on debating slavery.
D) President John Tyler's antislavery policies caused a major proslavery backlash led by John C. Calhoun.