How did sectionalism lead to the civil war? give at least one example and explain it.

It created loyalty for the states instead of the country

Explanation:

Sectionalism is the concept of one being more loyal to your region or state than to the country as a whole so when the country begins to tax your state or put regulations on a state that can infuriate you and make it harder to be loyal to the country thus creating a rift. This occurred when the north abolished slavery so the south's economy was hurt and the people supported their states over the country and thus became very upset over it.

might be agreeing to participate ethically with other european nations in the slave trade

or notifying other european nations when taking possession   of african territories