What did Ralph Waldo Emerson meant when he said "Mexico will poison us"

"Mexico will poison us" Emerson Waldo meant that although the United States had the power to conquer Mexico, the aftermath was not counter productive to its positive development. He feared that the ultra-expansionist ambitions of the United States were tainted by ulterior motives, which on the long run would only harm the country by dividing its people (Binder 49). Emerson was indeed right in a prophetic way. The word "poison" was used metaphorically to represent post war occurrences like slavery, which became pronounced after the war, and political divisions through out the country based on ideologies.