What problem did Frederick Jackson Turner's frontier thesis expose?

A.
America's unique development could not continue in the absence of a frontier.

B.
Intervention in international affairs would cause domestic interests to suffer.

C.
The U.S. Navy needed to be modernized.

D.
The purchase of Alaska was a bad idea.

A. America's unique development could not continue in the absence of a frontier.

The problem that Frederick Jackson Turner's frontier thesis exposed is represented by option A: America's unique development could not continue in the absence of a frontier. Turner argued that the closing of the American frontier in the late 19th century would have profound implications for American society and its identity. He believed that the frontier played a significant role in shaping American democracy, individualism, and the American spirit of opportunity and progress. With the frontier closing, Turner was concerned that these distinct qualities would diminish and that America would struggle to maintain its exceptional development without the presence of a frontier. To find the answer to this question, you can refer to primary sources such as Turner's writings, history books, or scholarly articles on the impact of the frontier thesis.

The problem that Frederick Jackson Turner's frontier thesis exposed was option A: "America's unique development could not continue in the absence of a frontier."