Final answer:
Frederick Jackson Turner attributed the development of American individualism and democracy to the frontier, as outlined in his Frontier Thesis. The frontier's challenges and opportunities fostered values of independence and egalitarianism, which were integral to America's national identity. Hence, "the frontier" (option e) is the correct answer.
Step-by-step explanation:
According to historian Frederick Jackson Turner, a key factor in the development of American individualism and democracy was e. the frontier. Turner's Frontier Thesis posited that the American frontier was a significant force in shaping the nation's character and democratic values. The frontier, as the interface between European traditions and the native wilderness, forced Americans into a situation where they had to be independent and self-reliant. This unique environment contributed to an egalitarian spirit while promoting values of hard work and independence.
The closing of the American frontier at the end of the 19th century, as declared by the 1890 US Census and Turner's subsequent analysis, raised important questions about the future of America's political culture and economic expansion. Turner viewed the frontier as 'the meeting point between savagery and civilization,' where American society was continually reinvented, influencing both western and eastern regions of the country.