Red Prophet by Orson Scott Card

160px-RedProphet(1stEd)

From Wikipedia:

Red Prophet (1988) is an alternate history/fantasy novel by Orson Scott Card. It is the second book in Card’s The Tales of Alvin Maker series and is about Alvin Miller, the seventh son of a seventh son. Red Prophet won the Locus Award for Best Fantasy Novel in 1989, was nominated for the Nebula Award for Best Novel in 1988, and the Hugo Award for Best Novel in 1989.