Ethnic and sectarian divides made the Iran-Iraq war multi-layered

Evidence

It could also be seen as a national conflict. One of the contestants—Iraq—is Arab. The other—Iran—is Persian. Though both Muslim, these are different peoples, speaking different languages, with different cultures. … It also had a religious dimension in that Iran is Shi‘a and is indeed ruled by a militant Shiite hierocracy while Iraq, though inhabited by a Shi‘a majority both in the country and in the capital, is ruled by a Sunni ascendancy. This was an important theme in the propaganda of the Iranians against Iraq during the war, and one naturally avoided by the Iraqis. — Bernard Lewis, From Babel to Dragomans, 1602