What is the purpose of this section of text?

Read this sentence from the text:

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.

What is the main purpose of this section of text?

To detail the sections that will follow.

To explain the period of time before the war.

To restate the main idea of this section.

To summarize the many causes of the war.