Monroe Doctrine asserted that any nation enacted any unwanted advances within the Western Hemisphere as an act of aggression toward the United States. The Monroe Doctrine states that any country has the right to defend itself from unwanted outside forces. The Monroe doctrine also promised to protect any other country within the Americas, should they be attacked or an attempt was ther made by any European country to colonize it. This was a very generous offer to all third world countries within the Americas. Likewise, America promised not to bother any already colonized country within the Western Hemisphere. This policy was was a direct result of Spain's aggression toward it's colony in Cuba.
Hope this helps :)
