The policy of the monroe doctrine was that the united states would not tolerate foreign intervention in and in return, the united states would stay out of european affairs.

Western Hemisphere 
It expressed three principles. First, the United States would oppose any further efforts at colonization by European powers in the Americas. This would not only be directed against Spain, but France who wanted Cuba, and at Russia who was seeking to expand its holding on the Pacific Coast. Second, the United States would abstain from involvement in the wars of Europe. Lastly, Monroe warned European powers not to interfere with the newly independent states of Latin America. The Monroe Doctrine is sometimes called America’s diplomatic declaration of independence. It claimed the United States role of dominant power in the Western Hemisphere.

South carolina was so angry about the election of lincoln that they seceded from the union on december 20, 1860. they attacked fort sumter later, on april 12, 1861.