When Europeans left home to settle America, the majority of them were of the Christian faith. Native Americans, better known as Indians at the time, had their own religions. Many of these were naturalistic religions, and not all of them were exactly the same. Most Native American religions involved Gods who cared for the land, and they described people as visitors. Each time an animal was taken for food or shelter, the people would thank the Gods for providing the animal.
Christianity has a long history of missionary work, and America was no different. The settlers brought their religion with them, and they worked at converting the locals to their own religion. Over the centuries, their work has been moderately successful. It is only in recent years that the Native Americans have turned back to their original religions, but many reservations still have Christian churches.