Athens used force to keep city-states from withdrawing from the league and <span>The purpose of the league was to keep Persia from conquering Greece.</span>
The correct answer is C. The closing of the western frontier.
In his 1893 published paper, The Significance of the Frontier in American History, Turner stated that while it was technically true that the frontier was closed, it was the frontier life that shaped the success of the United States. His idea, which was summarized in his frontier thesis, traced the development of the United States using the settlement of the West as a measure. He argued that early settlers were essentially Europeans; they had European values and European character, but because of the frontier experience, they had to adapt, resulting in their placing a greater value on things like ingenuity, democracy and individualism. Furthermore, it was these experiences of living out in the frontier that led to settlers becoming distrustful of authority, less artistic, and more violent.
