I wonder whether there's some confusion here between Monterey and Monterrey. Both were Mexican, and both were battle sites in 1846 during the war between the United States and Mexico, Monterey on 7 July, Monterrey 21 to 24 September. Monterrey is still Mexican, while Monterey, several hundred miles to the North, is in California, which was ceded to the US by Mexico as a result of the war.

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Thanks GerryM you may be right but the song title given is spelled “ Monterey “ so possibly it is with the songwriter that the confusion came in ?
Battle of Monterrey from Wikipedia    https://en.wikipedia.org/wiki/Battle_of_Monterrey