Churches in the South justified slavery and racism at some point, correct? Did this occur in the North as well? And if so, when?
Yes. Cotton Mather was a prominent minister in Massachusetts during the late 1600s, and even went so far as to preach to slaves that they were enslaved by God, not their masters, and their service was service to God. This ideology was later adopted by Ezra Stiles (as well as others) in the 1800s, who was a reverend in Connecticut.
Here is a copy of one of Mathers's pamhplets.