Over several decades beginning in 1620, tens of thousands of devout English colonists known as Puritans came to America. They believed that bringing Christianity to the natives would liberate them from darkness. Daniel Gookin, Massachusetts's missionary superintendent, called such efforts a "war of the Lord," a war in which Christ would deliver captive souls from Satan's bondage.

When Puritan soldiers slaughtered hundreds of indigenous men, women, and children at Fort Mystic in 1637, during the Pequot War, they believed they were doing God's will. The same was true during King Philip's War, perhaps the bloodiest war in American history. The Puritan clergyman Increase Mather described this conflict, too, as a "war of the Lord," a war in which God was judging the enemies of his people.

Matthew J. Tuininga argues that these two "wars" are inextricably linked. Puritan Christianity, he shows, shaped both the spiritual and military conquests of New England from beginning to end. It is not only that the people who did these things happened to be Christians; it is that Christianity was the framework they used to guide, interpret, and defend every major act of peace or war. They made sincere efforts to treat Natives according to Christian principles of love and justice as they understood them, and their sustained missionary efforts demonstrate how serious they were about saving native souls. Yet they appealed to Christianity just as confidently when they subjugated, enslaved, or killed native peoples in the name of justice. A mission they saw as spiritual, peaceful, benevolent, and just devolved into a military conquest that was virtually genocidal.

This book tells the story of how this happened from the perspective of those who lived it, both colonists and Native Americans.