Answer:
European nations respected the policies set forth in the Monroe Doctrine because they respected the United States as an equal and feared its powerful navy.
Explanation:
The Monroe Doctrine dates back to the State of the Union speech on December 2, 1823, in which President James Monroe drafted the broad outline of a long-term foreign policy before Congress. In the tradition of Jefferson, he found that the states on the American continent were irreversibly independent of the European powers.
Monroe formulated the existence of two political spheres. He emphasized the principle of the United States' non-intervention in European conflicts and called for an end to all colonization efforts in the western hemisphere (non-colonization). He also announced that the United States would intervene in the event that the European colonial powers ignored these political principles. The demand on the European powers not to recolonialize the now independent states of Latin America has been shortened to the slogan "America to the Americans".
The European nations were already warned of the American military power, which had defeated the British forces in 1815, thus confirming American supremacy on the continent. Therefore, and in view of the conflicts that these countries had within Europe, the European nations decided to accept this Doctrine.