Answer:
A. to respond to events that threatened the United States
Explanation:
The Monroe Doctrine basically says that if Europe tried to get involved in the west's business or tried to colonize in the Americas any further, the United States would see it as a threat. SO if Europe stayed out of American affairs in the west, the U.S would stay out of European affairs in the East. This provided security for the U.S and gave the U.S justification to attack any European countries if they did something that the United States saw as a threat.
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