Which best explains the message the Monroe doctrine sent to other nations
Assuming that this is referring to the same list of options that was posted before with this question, the correct response would be that the Monroe Doctrine sent a message to European powers that any further intervention in the Americas would be seen as an act of aggression, since the US felt that its interests were being threatened.
Answer: is A, that the United States was powerful enough to stop new colonization in the Americas.