Final answer:
Frederick Jackson Turner's Frontier Thesis argued that the American frontier was essential in shaping national identity and values. It was provocative because it suggested that with the frontier's closure, America's future character was uncertain. Critics believe the thesis oversimplified and overlooked Native Americans' contributions.
Step-by-step explanation:
Frederick Jackson Turner’s Frontier Thesis posited that the American frontier was integral in shaping the nation’s character and democracy. Introduced in 1893, Turner’s thesis suggested that the continual expansion westward fostered a spirit of innovation and egalitarianism. However, Turner also claimed that, with the closing of the frontier as there was no longer land readily available for expansion, the United States might lose this defining characteristic of its identity. This idea was considered provocative as it brought into question the future of American culture and its ability to sustain its unique values without the influence of the frontier experience. Critics later argued that Turner’s thesis oversimplified the contributions of Native Americans and the complexities of frontier life.