In what ways does the dispute over protective tariffs illustrate a growing sectionalism in the united states?

Sectionalism divides a country's loyalties according to the local interests of each section or region.

If you had used the past tense in your question, I might think you were talking about the sectionalism that occurred in the Civil War era.  The South was against tariffs because they relied on the import of British goods.  The North supported tariffs to protect their homegrown industries.

Since you asked your question in the present tense, however, I'll assume you're talking about the present day.  But the same principle holds as was illustrated in the Civil War era.  Sectionalism is the division of the country section by section -- one section or area having interests that conflict with those of other sections or regions.  So, for instance, the US president recently announced a plan to impose heavy tariffs on steel imports.  That sort of policy is supported in areas like Pennsylvania where US steel production is centered.  But such tariffs are opposed in other sections of the country and other sectors of industry that rely on affordable steel in making their products -- such as automobiles.