Which excerpt best states the central idea of the second paragraph of the dark game?

most of the war was fought in states south of washington, d. c. .
for the union soldiers, this meant they had to fight in unfamiliar and hostile territory.
this matter of geography affected the spies who worked behind enemy lines.
confederate spies could usually find a safe house, or at least a sympathetic soul . .

The best idea of the second paragraph is that this matter of geography affected the spies who worked behind the enemy lines

Explanation:

This was a true story which was written inspired by the lives of two spies and this uncovers two centuries worth stories with the technology involved

Many spies were always there to report the conditions upon the two nation their progress and their economic status and the main central idea f the second passage is that many enemies worked behind the geographical borders

now you can make him brainleist.              

which one is underlined?