In the second sentence in part 2 of "An Occurrence at Owl Creek Bridge," the word "secessionist" is used. What does that sentence mean?

"An Occurrence at Owl Breek Bridge" is set during the American Civil War, when the North and South fought over many things, but most importantly, slavery.  The main character of the story, Peyton Farquhar, is described as "a well-to-do planter, of an old and highly respected Alabama family" and a slave owner.  Politically-speaking, then, he sides with the South in their wanting to keep slavery as an economic right.  The South wanted to secede, or split, from the rest of the country and create their own country, which is why they had their own President for a time, Jefferson Davis.  In the context of this story, Farquhar is a proud Southern plantation owner who has devoted himself to their cause from the beginning.  This information is important to the story because it is this fervor for the Southern cause that persuades him to attempt to blow up the Owl Creek Bridge, which he was tricked into doing by a Federal scout (mentioned in the last sentence of Part II); the Federal scout is on the Northern side, but he was dressed in grey, which was the uniform of the Confederates (the South).