What dose the term sectionalism mean

Sectionalism generally means being loyal to only a part, instead of the whole.

Explanation:

Examples can be seen more in a country term, taking the US for example. People in California may be more loyal to California and may put state priorities in front of national securities. Another example can be the South, which mostly contain rural townspeople and farmers, and they may be loyal to only politicians who can support their way of life. This is a "section" of people who are only loyal to a person because of such & such benefit.