Saddam Hussein’s goal for attacking Iran was to conquer Iranian oil fields.
Saddam was thinking that (Sunni) Arab Iranians would be oppressed in Iran (as Shia are oppressed in many Arab countries) and would join forces with their Arab “brothers” from the Iraqi Army, but the opposite was the case Arab Iranians felt more as Iranians than as Arabs and fiercely defended their homeland Iran and stopped the mighty Iraqi Army until the surprised Iranian army could finally send help to the Iraqi border.
This story beautifully shows how Arab leaders speculated and finally invented an oppression of the (Sunni) Arab minority in Iran, and were surprised by the realities on the ground, that these allegedly oppressed minorities felt pretty much Iranian, and nearer to their fellow Shia Iranians than to external Sunni and even Shia Arabs.
Great book that covers the Iraq-Iran war and other conflicts in the Middle East:
100words 