Pictures of dogs resembling the modern Chihuahua appear in ancient paintings in Mexico Since the 1960s, the Chihuahua has been one of the most popular breeds in the world. No one knows for sure the Chihuahua's origin but there are two main theories. For the first we need to look back to the Toltec and Aztecs civilizations. Many people believe that the breed descended from a South American dog known as the Techichi. There are Toltec carvings dating to the 9th century C.E. that depict a dog resembling the Chihuahua. The Spanish conquered the Aztecs in the late 1500s and the Techichi disappeared.
The second theory is that small dogs with smooth coat from China were brought to Mexico by European traders and bred with other small native dogs afterwards. The long-coat chihuahua was probably created through crosses with Papillon or Pomeranian many years after that .Regardless of which theory is accurate, the shorthaired Chihuahuas we know today were discovered in the 1850s in the biggest state in north Mexico called Chihuahua, from which they had their name. Just a decade later the Americans started to bring the dogs with them and first registered chihuahua with American Kennel Club was in 1904.