"confinement of interests to a local sphere," but originally "sectional prejudice or spirit; the clashing of sectional interests," 1836, American English, from sectional + -ism. In frequent use from 1856.
1806, "pertaining to a division of a larger part;" see section (n.) + -al (1). Originally and especially "of or pertaining to some particular section or region of a country as distinct from others," in which sense it loomed large in the U.S. political vocabulary in the decades before the Civil War.
The meaning "composed or made up of several independent sections that fit together" is by 1875, originally mechanical. The noun meaning "piece of furniture composed of sections which can be used separately" is attested by 1961, short for sectional seat, sectional sofa, etc. (1949).
word-forming element making nouns implying a practice, system, doctrine, etc., from French -isme or directly from Latin -isma, -ismus (source also of Italian, Spanish -ismo, Dutch, German -ismus), from Greek -ismos, noun ending signifying the practice or teaching of a thing, from the stem of verbs in -izein, a verb-forming element denoting the doing of the noun or adjective to which it is attached. For distinction of use, see -ity. The related Greek suffix -isma(t)- affects some forms.
<a href="https://www.etymonline.com/word/sectionalism">Etymology of sectionalism by etymonline</a>
Harper, D. (n.d.). Etymology of sectionalism. Online Etymology Dictionary. Retrieved $(datetime), from https://www.etymonline.com/word/sectionalism