Final answer:
President Monroe's opposition to European colonialism was ironic because he reserved the United States' right to interfere in Latin American affairs while opposing European interference, as stated in the Monroe Doctrine. Therefore, the correct option is B.
Step-by-step explanation:
The irony of President Monroe's opposition to European colonialism was that he reserved the United States' right to interfere in Latin American affairs while opposing European interference. This is known as the Monroe Doctrine, which stated that the United States would guarantee the independence of nations in the Western Hemisphere and warned European nations to refrain from interfering with independent countries in the Western Hemisphere.
An example of this irony can be seen in President Roosevelt's interpretation of the Monroe Doctrine, known as the Roosevelt Corollary. Under this interpretation, the United States believed it had the right to intervene in the affairs of independent nations throughout the Western Hemisphere. This demonstrated the delicate balance between opposing European colonialism while reserving the right to exert influence in the region.