Both spirit and spirits are correct because spirit, being singular, means all the citizens of the country as one. Spirits is plural which means spirits of all the citizens of that nation.
When Scout puts up a question to her father, to that Atticus replied,
"It's slipped into usage with some people like ourselves when they want a common, ugly term to label somebody."
Atticus is very preventive about his kids, Jim and Scout. He didn’t like his kids face the world’s ugliness and does his best to protect them. To this he opens the door, explains how nasty people can be by taking the case of Tom Robbins. Atticus explains to them that doing the right thing and taking the stand for the right is difficult but results in the best.
The answer is in the link below
xtiny.527//.com