Dogs, wolf-like canids believed to be related to an extinct species of wolf, are known to have been with us for 15,000 to 35,000 years. Humans from Siberia who crossed the Bering Strait when still a land bridge more than 10,000 years ago are believed to have had dogs in their company. Those dogs perhaps even made the human migration possible by pulling sleds. These are thought to be the common primogenitors to all American dog breeds.
Another huge influence on American breeds, and substantially more recent, were those pets and working dogs brought to America by early explorers and colonists. Many of these immigrant dogs most likely bred with native American dogs, creating still more new types to be ultimately bred for special purposes and domesticated further.