The monroe doctrine stated that the united states would
a. oppose european attempts to colonize nations.
b. encourage european attempts to colonize nations.
c. take control of existing european colonies.
d. interfere in european conflicts.

The correct answer is A) oppose European attempts to colonize nations.

The Monroe Doctrine stated that the United States would oppose European attempts to colonize nations.

On December 2nd, 1823, United States President James Monroe addressed the Congress and informed about the Monroe Doctrine foreign policy. The main points of the Monroe doctrine were that the United States was not going to interfere with the internal affairs between countries in Europe, the U.S. was not going to interfere with the actual European colonies in the Western Hemisphere, that region of the world was not going to be colonized by any other country, and finally, if a European country tried to control any nation in the Western Hemisphere, the United States would view that attempt as a hostile act.  

The right answer is: A) Oppose European(...)colonize nations. The Monroe doctrine, synthesized in the quote "America for the Americans", was elaborated by John Quincy Adams and attributed to president James Monroe in 1823. It established that any European intervention in America would be seen as an act of aggression that would require intervention of the United States of America.  It was a decisive moment in the foreign policy of the United States representing its opposition to colonialism in response to the threat posed by the monarchical restoration in Europe and the Holy Alliance after the Napoleonic wars.

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explanation:

porter is writing economic history because he is focusing on the cost of developing vaccines.