Answer:
Option C, the closing of the western frontier, is the right answer.
Explanation:
An argument that claimed that American democracy was established by the American frontier came to be known as the Frontier Thesis. This argument was presented by historian Frederick Jackson Turner in the year 1893. He argued that the primary result of the American frontier was American democracy along with a lower interest in high culture, violence and egalitarianism.
Wait, who lived in that time? The answer could be 'war' but I need more information...
The Truman Doctrine underpinned American Cold War policy in Europe and around the world. The doctrine<span> endured because it addressed a broader cultural insecurity regarding modern life in a globalized world.
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