Mexico

Mexico is a nation in North America. The Doctor, Susan, Ian Chesterton and Barbara Wright visited Mexico in 1454. Barbara attempted (and failed) to alter the history of the Aztecs. (DW: The Aztecs)

The War Lords kidnapped several soldiers from the Mexican Uprising of 1867 for use in their War Games. (DW: The War Games)

The Doctor, Ace and Bernice Summerfield visited Mexico in 1994. (NA: The Left-Handed Hummingbird)

Mexico was the birthplace of attempted dictator Ramón Salamander. (DW: The Enemy of the World)

In the alternate reality of Pete's World, as the United States of Mexico, the country still extends up to Arizona - implying its victory in the 1840s Mexican-American War - and is run by a Prime Minister. (Cybus Industries tie-in website)