The answer is C Or D: You can pick based on my answers. I got this answer by using the process of elimination.
Lack of cultural identity; The United States had a sense of cultural identity during this time.
economic instability: The U.S was partially stable, during the mid 19th century they had a ton of economic instability. I say this is wrong because the beginning and end of the 19th centuries were prosperous.
political instability: Yassss! They were unsure if they should help the European countries or if they should stay out. This was called isolationism.
geographic isolation: This could be, but Canada, Japan, Australia, and many other far countries joined the war. This might be the answer because the U.S stated they would only interfere in Western conflict.