During the 19th century, the united states ability to remain isolated from european affairs was largely due to its
a. lack of cultural identity.
b. economic instability.
c. political instability.
d. geographic location.

I would say that the location is the major reason why the United States managed to stay isolated - it is separated by two big bodies of water (the Atlantic and the Pacific Ocean) and specifically, it is separated by the Atlantic Ocean from Europe -this allowed it to say  away from the European affairs.

I’m pretty sure it’s 4, you can check on the calculator