Even though Mexico is in North America, it was colonized by the Spanish who also colonized most of South and Central America. This is in contrast to both Canada and the United States which were colonized by the British.
The Spanish had a policy of assimilating indigenes into Spanish Culture as much as possible leading to a large number of intermarriage. This led to the many groups in Spanish territories having similar attributes such as the speaking of Spanish, religion mostly being Catholicism and various other attributes.
This is why Mexico is closer to countries in South America than North.
