Answer:
The correct option is D) westward migration
Explanation:
Frederick Jackson Turner was of the view that the frontier shaped the culture, society and institutions in America.
He believed that the Frontiers and the westward march of the pioneers from the Atlantic to the Pacific Coat, distinguished the Americans from the Europeans.
He thought that the movement of the settlers in the West of America  was the reason behind the exceptional character changes in the Americans.  Frederick Jackson Turner influenced the American political leaders during the 20th century.
