What role did religious differences play in the iranian revolution and the iran -iraq war?

Difference of government philosophy and differing sects of Islam. 

For the Iranian Revolution, the question of a secular versus religious government was of concern. The government being overthrown was more secular and Western influence was there. The revolutionaries were fundamentalists who wanted religion to return to the government.

In the Iraq-Iran War, it was a difference of religious sides within Islam. Iraq is more Sunni and Iran is more Shi'a. These sects have a long history of conflict and the difference in religion and politics influenced the war. Also the question of western influence in the area was of concern.