My approach is generally to point to scholars who know this better than I do! Antebellum southerners used Christianity to justify every element of slavery; antislavery activists likewise drew on Christianity to show that slavery was a sin. Some books on the topic:

Charles Irons, The Origins of Proslavery Christianity
Rebecca Goetz, The Baptism of Early Virginia: How Christianity Created Race
Ben Wright, Bonds of Salvation: How Christianity Inspired and Limited American Abolitionism