Question

Sectionalism can BEST be defined as

Answer 1

the loyalty to one's own region or part of the country, rather than to the country as a whole.

Say, being passionate about your home state or even hometown rather than being passionate about the USA. 

Answer 2

BEFORE WE START:
Sectionalism has quite a few definitions. I don't know what it means, but I'm willing to do some research and provide you with the best definition.

DEFINE SECTIONALISM:
→When you are loyal to someone's region or their section of a country (if they're not "over" an entire country). 
→"Undue concern with local interests or petty distinctions at the expense of general well-being" -Google

WHY TWO DEFINITIONS?
This word could mean a few different things depending on how you use it, so I'm going to leave it up to you to find out which definition you want to use.