Reread these lines from the Chapter 1 excerpt and answer the question that follows:

And this great crisis was only the bursting into flame of many smaller fires that had long been smoldering. For generations the two sections had been drifting apart. Since the middle of the seventeenth century, Mason and Dixon's line had been a line of real division separating two inherently distinct portions of the country.

Which of the following best summarizes the main message of these lines?

A. The two sides of the country were irreconcilably different.

B. The two sides of the country should never have been together.

C. The great crisis was caused by Mason and Dixon's division.

D. The great crisis was the result of long-building tensions.