In 1947, President Harry S. Truman pledged that the United States would help any nation resist communism in order to prevent its spread. His policy of containment is known as the Truman Doctrine.
It helped because it enabled other fronts to open up because the American Offensive in the area ended with a victory, which meant that they could move to other areas and bother Germans there. They didn't' do this however because the fighting ended since the Germans became aware of their losses and signed an armistice.
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The Monroe Doctrine simply stated that the west will not interfere with the affairs of Europe as long as they didn't interfere with us. This enabled us to be able to deal with the smaller countries and help them reform their government. The Monroe doctrine allowed the United States to become "protectors" of the smaller countries in the western hemisphere.
