Answer: a. Northern and Southern states developed significant differences on key issues.
Step-by-step explanation:
Sectionalism refers to people in a country becoming loyal to the ideals and way of life of their part of the country even if this conflicts with other parts of the country.
Before civil war engulfed the United States, the industrial North and the agricultural South had developed different ways of thinking that led to them disagreeing on key issues chief amongst them being slavery. It was this sectionalism that led to the Civil war.