In the decades before the Civil War, evangelical Protestants struggled for the mind and soul of America. Their impact on American life had immediate as well as far-reaching consequences, and is the subject of Curtis Johnson's concise and discerning account of a major force in the nation's history. The religious combatants described by Mr. Johnson not only sought to rescue America from Catholics and unbelievers, they battled one another over the meaning, practice, and social implications of their common faith. While prosperous evangelicals often tried to impose their religious understanding on...